Fire load is the total heat the contents of a room, floor or building could release if they all burned, measured in megajoules. NBCS 2026 Part F defines it in clause 2.25, and IS 1641 also counts the building's own combustible parts.

What is fire load density?

Fire load density is the fire load divided by the floor area, in MJ/m² or in kg of wood equivalent per m². Part F gives typical values: about 25 kg/m² for homes, 25 to 50 for offices and up to 500 for storage.

What is the formula for fire load calculation?

Multiply the mass of each combustible material by its calorific value, add the results, and divide by the floor area. A 20 m² office with 400 kg of wood at 17.6 MJ/kg has 7,040 MJ from the wood alone, or 352 MJ/m².

What is the unit of fire load?

Megajoules (MJ) for fire load and MJ/m² for fire load density in NBCS 2026. The older IS 1641:1988 used kilocalories per m². Part F also expresses density as kg of wood equivalent per m².

What calorific value of wood should I use?

17.6 MJ/kg, the value in NBCS 2026 Part F Annex A, Table 12, for hard or soft wood. It is also the 1.00 on the wood-equivalent scale the table uses for every other material.

Which IS code covers fire load?

IS 1641, on fire grading and classification; the current edition is IS 1641:2013. NBCS 2026 Part F carries the working definitions, the density table and the calorific values in Annex A.

What is the fire load density of an office?

Part F puts business buildings at 25 to 50 kg of wood equivalent per m², about 440 to 880 MJ/m². A 2018 survey of offices and dormitories in Ahmedabad reported about 1,400 MJ/m² on average.

What is the difference between fire load and occupant load?

Fire load is the energy stored in what can burn. Occupant load is the number of people a floor is designed for, used to size exits. Both appear in Part F, but they size different things.

Fire safety glossary 16 min read

Fire load and fire load density: the formula, the calorific values and how they set a building's hazard class

Updated October 2026By Flamekite Editorial DeskFacts checked against official sources on 24 October 2026

Quick answer

Fire load is the heat a space's contents can release, in MJ; divide it by floor area for fire load density. NBCS 2026 uses wood at 17.6 MJ/kg as the yardstick (Part F, clauses 2.25 and 2.26, and Annex A).

The formula is the mass of each combustible multiplied by its calorific value, added up and divided by the floor area. Part F puts homes at about 25 kg of wood equivalent per m² and storage up to 500. The fire authority uses the result, with the processes and finishes, to set the hazard class that sizes sprinklers and pumps.

Wood, the yardstick: 17.6 MJ/kg; Wood equivalent 1.00 in Table 12; Calorific values
Homes: 25 kg/m²; Of wood equivalent, about 440 MJ/m²; Density table
Storage and hazardous: Up to 500 kg/m²; The highest band in Part F; Density table
Modern offices measured: 1,400 MJ/m²; 2018 survey, about 3 times older data; Numbers

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Fire load at a glance

What the national standard, the older IS code and a state rule say fire load is, with the source of each line.
What	The rule	Source
Fire load	The total energy that could be released in a fire in a compartment, floor or building, usually in megajoules (NBCS 2026 Part F, clause 2.25)	BIS, SP 7:2026
Fire load density	Fire load divided by the floor area of that compartment, floor or building, in MJ/m² or in kg of wood equivalent per m² (clause 2.26)	BIS, SP 7:2026
Formula	Mass of each combustible multiplied by its calorific value, added up, divided by the floor area (IS 1641:1988, clause 2.2)	IS 1641:1988
What counts	The contents and any combustible parts of the building itself (IS 1641:1988, clause 2.1)	IS 1641:1988
In state law	Tripura's Fire Safety Rules, 2026 define it as the calorific energy of everything in a space, including the facings of walls, partitions, floors and ceilings	Directorate of Fire and Emergency Services, Tripura
Calorific values	Annex A, Table 12 of Part F lists 71 materials in MJ/kg and in wood equivalent	BIS, SP 7:2026
Wood	17.6 MJ/kg, wood equivalent 1.00	BIS, SP 7:2026
Who uses it	The fire authority sets the hazard of occupancy from the fire load of the contents and the processes in the building (clause 3.1.8)	BIS, SP 7:2026
Current IS code	IS 1641:2013, general principles of fire grading and classification, current on the BIS database to 31 July 2028	BIS standards database

Fire load in IS 1641:1988 and NBCS 2026

How the older Indian Standard and the 2026 national standard describe fire load.
Option	IS 1641:1988	NBCS 2026 Part F	Source
Unit	Kilocalories per m² of floor	Megajoules, or kg of wood equivalent per m²	IS 1641:1988
What is counted	The contents and any combustible parts of the building	The energy that could be released in the compartment, floor or building	IS 1641:1988
Calorific value table	Deleted in this revision as available in textbooks	Annex A, Table 12, 71 materials	IS 1641:1988
Typical densities by building type	None given	Homes 25 kg/m² up to storage 500 kg/m² of wood equivalent	BIS, SP 7:2026
Who sets the hazard class	The authority, from the character of the contents and the processes; the greater hazard governs	The authority, from the fire loads of the contents and the processes (clause 3.1.8), with Annex B for industry	IS 1641:1988
Status on 24 October 2026	Superseded by IS 1641:2013	Current, since 30 April 2026	BIS standards database

How to calculate fire load, step by step

Mark the compartment and its floor area
Work room by room or compartment by compartment, not over a whole building: a 20 m² office and a 500 m² godown give very different densities.
List every combustible by material
Weigh or estimate furniture, stock, packaging and paper, and add the building's own combustible parts such as partitions, false ceilings and floor finishes.
Take each calorific value from Table 12
Use NBCS 2026 Part F Annex A: wood 17.6 MJ/kg, paper 15.4, polyethylene 48.4, PVC 20.9 and so on.
Multiply and add
Mass in kg multiplied by MJ/kg gives MJ for each material. The total is the fire load in MJ.
Divide by the floor area
MJ divided by m² is the fire load density. Divide it by 17.6 to express it as kg of wood equivalent per m², the unit of Part F's density table.
Check concentrations separately
Work out each tall stack or store on its own floor area as well, because the average hides it.
Hand it to the authority with the processes
Give the result to the fire authority together with the processes and the finishes. It sets the hazard class, which picks the protection level and the pump size.

Fire load density by building type in NBCS 2026

Flamekite’s working from the official rules; no government publishes this figure.

Clause 2.26 of Part F gives a typical fire load density for each occupancy, in kg of wood equivalent per m². The MJ column is Flamekite's conversion at 17.6 MJ/kg.

	Wood equivalent (kg/m²)	About MJ/m² at 17.6 MJ/kg
Residential (A) BIS, SP 7:2026	25	440
Educational and institutional BIS, SP 7:2026	25	440
Assembly (D) BIS, SP 7:2026	25 to 50	440 to 880
Business (E) BIS, SP 7:2026	25 to 50	440 to 880
Mercantile (F) BIS, SP 7:2026	Up to 250	Up to 4,400
Industrial (G) BIS, SP 7:2026	Up to 150	Up to 2,640
Storage (H) and hazardous (J) BIS, SP 7:2026	Up to 500	Up to 8,800

Proof-read from page 13 of Part F. The table prints Institutional as (B) and Educational as (C), the reverse of the group letters in clause 3.1, where B is educational and C institutional; the values are the same for both.

Fire load calorific values from NBCS 2026 Annex A

Sixteen common materials from Table 12, in MJ per kg and in kg of wood each kg equals. Plastics release two to three times the heat of wood.

Wood, hard or soft: 17.6 MJ/kg; wood equivalent 1.00, the yardstick for the table. BIS, SP 7:2026
Paper, average: 15.4 MJ/kg; 0.88. BIS, SP 7:2026
Cotton, dry: 15.8 MJ/kg; 0.90. BIS, SP 7:2026
Leather: 17.6 MJ/kg; 1.00. BIS, SP 7:2026
Polyethylene: 48.4 MJ/kg; 2.75. BIS, SP 7:2026
Polypropylene: 48.4 MJ/kg; 2.75. BIS, SP 7:2026
Polystyrene: 41.8 MJ/kg; 2.38. BIS, SP 7:2026
Polyurethane (foam in seats and mattresses): 35.2 MJ/kg; 2.00. BIS, SP 7:2026
Polyvinylchloride (PVC): 20.9 MJ/kg; 1.19. BIS, SP 7:2026
Rubber: 37.4 MJ/kg; 2.13. BIS, SP 7:2026
Fuel oil: 41.6 MJ/kg; 2.36. BIS, SP 7:2026
Propane: 47.3 MJ/kg; 2.69. BIS, SP 7:2026
Ethyl alcohol: 28.4 MJ/kg; 1.61. BIS, SP 7:2026
Bituminous coal: 30.8 MJ/kg; 1.75. BIS, SP 7:2026
Sugar: 15.4 MJ/kg; 0.88. BIS, SP 7:2026
Rice: 13.9 MJ/kg; 0.79. BIS, SP 7:2026

Fire load calculation: 3 worked examples

Flamekite’s working from the official rules; no government publishes this figure.

Flamekite's arithmetic with the Table 12 values. The masses are illustrations, not survey data.

Case 1
A 20 m² office
400 kg of wooden furniture, 300 kg of paper, 20 kg of polyurethane seat foam and 30 kg of polyethylene and polypropylene items.
What applies 7,040 + 4,620 + 704 + 1,452 = 13,816 MJ of fire load. Divided by 20 m², that is 690.8 MJ/m², or about 39 kg/m² of wood equivalent: inside Part F's 25 to 50 kg/m² for business buildings. BIS, SP 7:2026
Case 2
A 500 m² cotton godown
40,000 kg of cotton bales, 5,000 kg of polyethylene wrap and 2,000 kg of wooden pallets.
What applies 632,000 + 242,000 + 35,200 = 909,200 MJ. Over 500 m² that is 1,818 MJ/m², or 103.5 kg/m² of wood equivalent: inside the storage band of up to 500 kg/m². BIS, SP 7:2026
Case 3
The same godown, stacked in one corner
All 909,200 MJ of stock on 100 m² of the 500 m² floor.
What applies Over the stacked area the density is 9,092 MJ/m², five times the floor average. IS 1641 warns that an average over the whole floor misrepresents a concentrated load, so assess the stack on its own. IS 1641:1988

Fire load numbers worth knowing

17.6 MJ/kg
Calorific value of wood, the 1.00 of the wood-equivalent scale BIS, SP 7:2026
48.4 MJ/kg
Polyethylene and polypropylene, 2.75 times wood BIS, SP 7:2026
71
Materials with calorific values in Part F Annex A, Table 12 BIS, SP 7:2026
500 kg/m²
Top of Part F's density range, for storage and hazardous buildings BIS, SP 7:2026
1,400 MJ/m²
Average fire load found in 105 office rooms and 202 dormitory units in Ahmedabad, reported in 2018 Down To Earthnews report
487 MJ/m²
Average from a Kanpur survey about 20 years earlier, a third of the 2018 figure Down To Earthnews report

From fire load to sprinkler and pump size

Fire load is the first link in a chain that ends in a pump's litres a minute.

1. Fire load and density
The contents survey gives MJ, and MJ per m² (clauses 2.25 and 2.26). BIS, SP 7:2026
2. Hazard of occupancy
The authority sets it from the fire load and the processes; where finishes or materials are more dangerous, the greater hazard governs (clause 3.1.8). BIS, SP 7:2026
3. Industrial class
Annex B sorts industries into G1 low, G2 moderate and G3 high hazard by fire hazard only: an agarbatti unit is G1, a bakery G2, a fireworks unit G3. BIS, SP 7:2026
4. Protection level
Tables 7A to 7J give each building a level: HL-1 to HL-6 for hose only, CL-1 to CL-8 with sprinklers. BIS, SP 7:2026
5. Pump size
Table 7K adds 20% to the total flow and divides by 1.4. For CL-5, 4,231 becomes 5,077.2 and then 3,627 lpm, so the nearest standard pump is 3,785 lpm, with an equal standby and a jockey pump. BIS, SP 7:2026
6. Sprinkler spacing
Mizoram's 2026 rules space heads by hazard: 12 m² a head for light hazard, 9 to 12 m² for ordinary and 6 to 9 m² for high, with the hazard terms as in IS 15105; IS 15105:2021 itself allows up to 21, 12 and 9 m² a head (cl. 9.17.1), so Mizoram is stricter. Mizoram Home Dept

Fire load hazard levels in NBCS 2026 Table 7K

Eight combined levels, from extra low to high hazard, each with its hose streams, its pump and its duration. The hose flow is at 3.5 bar.

CL-1
Extra low hazard 1
2 hose streams of 50 lpm; a 379 lpm pump; 30 to 60 minutes. BIS, SP 7:2026
CL-2
Extra low hazard 2
2 streams of 170 lpm; a 946 lpm pump; 30 to 60 minutes. BIS, SP 7:2026
CL-3
Low hazard
3 streams of 285 lpm; a 1,892 lpm pump; 30 to 60 minutes. BIS, SP 7:2026
CL-4
Moderate hazard 1
3 streams of 285 lpm; a 2,500 lpm pump; 60 to 120 minutes. BIS, SP 7:2026
CL-5
Moderate hazard 2
3 streams of 475 lpm; a 3,785 lpm pump; 60 to 120 minutes. BIS, SP 7:2026
CL-6
Extra hazard 1
3 streams of 475 lpm; a 4,731 lpm pump; 60 to 120 minutes. BIS, SP 7:2026
CL-7
Extra hazard 2
4 streams of 670 lpm; a 7,570 lpm pump; 60 to 120 minutes. BIS, SP 7:2026
CL-8
High hazard
4 streams of 1,050 lpm; two pumps of 4,731 lpm; 60 to 120 minutes. BIS, SP 7:2026

Who decides the fire load hazard class?

No owner self-assigns a hazard class. Find the line that matches your building.

If Your building's contents are the main fire risk
The fire authority sets the hazard of occupancy from their fire load and from the processes carried on (clause 3.1.8). BIS, SP 7:2026
If Its finishes or materials burn faster than the contents suggest
The greater hazard governs the class, whatever the fire load works out to. BIS, SP 7:2026
If It is a factory named in Annex B
It takes that class, G1, G2 or G3; a factory not named goes in the most fitting class. BIS, SP 7:2026
If It is in Tripura
The Fire Safety Rules, 2026 carry the same rule in Schedule I, clause 1.1.8, with their own definition of fire load. Directorate of Fire and Emergency Services, Tripura
If It is in Assam and Schedule I does not list it
Section 23(2) of the 2025 Act classes it by fire load, construction, combustibility and flame spread. Fire NOC Assam 2026 Assam Act LIII of 2025
If It is a tall building in Chandigarh
Section 18(4) makes height no bar by itself if protection matches the occupancy risk and fire load. Fire NOC Chandigarh Gazette of India
If It is an industry in Andhra Pradesh
Its hazard class sets the renewal period: 5 years for low, 3 for moderate and 2 for high hazard. Fire NOC Andhra Pradesh G.O.Ms.No.178

Mizoram writes cumulative fire load into its rules

Mizoram's 2026 amendment lets an industrial estate hold one common fire NOC, on one condition about fire load.

Word for word

The common fire protection system is designed taking into consideration the cumulative fire load and occupancy of the entire complex;

Mizoram Fire and Emergency Services (Superintendence and Control of the Fire Force and Fire Safety and Prevention) (Amendment) Rules, 2026, rule 57(A)(d), Notification No. B-20011/2/2026-HM(F&ES), 20 August 2026 Mizoram Home Dept

The same notification uses fire load twice more: rule 57(8) lets the Director ask for more or relax a requirement having regard to occupancy, height, fire load, site and access, and rule 57(B)(4) lets him change the technical requirements on the same grounds.

Fire load class and Assam's fines

In Assam the vulnerability class, which section 23(2) ties to fire load for unlisted buildings, sets the fine for occupying without a certificate.

Offence	Penalty	Law
Occupying a low vulnerability building without a Fire Safety Certificate	Rs 10,000 to Rs 25,000	Section 26(2) Assam Act LIII of 2025
Occupying a moderate vulnerability building without one	Rs 25,000 to Rs 50,000	Section 26(3) Assam Act LIII of 2025
Occupying a high vulnerability building without one	Rs 1 lakh to Rs 5 lakh, plus up to Rs 5,000 a day	Section 26(4) Assam Act LIII of 2025

Assam Fire and Emergency Services Act, 2025 (Act LIII of 2025). Schedule I lists building types by class; Flamekite's Assam page has the full schedule.

Fire load in Indian codes, 1960 to 2026

1960
IS 1641, the code on fire grading and classification, is first issued. IS 1641:1988
2 May 1988
BIS adopts the first revision of IS 1641. It defines fire load in kcal per m² and deletes the calorific value tables as available in textbooks. IS 1641:1988
1997
Amendment No. 3 to the 1983 NBC adds an annex on fire loads and calorific values, and one classing occupancies into low, moderate and high hazard. BIS, SP 7:2026
31 July 2013
IS 1641:2013 is published; it is the current edition. BIS standards database
9 August 2018
An IIT Gandhinagar survey reports about 1,400 MJ/m² in modern offices and dormitories. Down To Earthnews report
24 December 2025
Assam's new fire Act classes unlisted buildings by fire load. Assam Act LIII of 2025
30 April 2026
NBCS 2026 Part F defines fire load in MJ and keeps the calorific value annex. Gazette of India
2 June 2026
Tripura's Fire Safety Rules, 2026 define fire load and fire load density in state law. Directorate of Fire and Emergency Services, Tripura
20 August 2026
Mizoram's amendment requires common systems to be designed for cumulative fire load. Mizoram Home Dept

Fire load calculation mistakes

Each of these understates or misstates the fire load an officer will check.

If Averaging one tall stack over the whole floor
Work out the stack on its own area as well; IS 1641 says an average misrepresents a concentrated load. IS 1641:1988
If Leaving out the building's own combustible parts
Count partitions, false ceilings and floor finishes, as IS 1641 and Tripura's definition both include them. IS 1641:1988
If Using one value for every plastic
PVC is 20.9 MJ/kg and polyethylene 48.4: take each material's own line in Table 12. BIS, SP 7:2026
If Comparing kg/m² with MJ/m²
Part F's density table is in kg of wood equivalent; multiply by 17.6 to get MJ/m². BIS, SP 7:2026
If Treating fire load as the whole hazard
Materials of equal weight and heat still differ in ease of ignition, burning speed and fumes; the authority weighs those too. IS 1641:1988
If Assuming the old survey figures still hold
A 2018 survey found about 3 times the fire load of earlier Indian data; measure, do not assume. Down To Earthnews report

Four fire load myths

You may have read
Fire load only matters for factories.
Myth
What the sources say
Part F gives a typical fire load density for every building type, from 25 kg/m² for homes upward. BIS, SP 7:2026
You may have read
Fire load means the number of people in a building.
Myth
What the sources say
That is occupant load. Fire load is energy, in MJ, from what is stored and built in. BIS, SP 7:2026
You may have read
IS 1641 sets low fire load below 2,75,000 kcal/m².
Myth
What the sources say
Those bands are widely quoted, but they are not in the 1988 text of IS 1641, which gives the method only. IS 1641:1988
You may have read
A low fire load means no sprinklers.
Myth
What the sources say
Height and floor area trigger sprinklers too: Table 7A asks for them in every apartment tower above 60 m. BIS, SP 7:2026

Fire load survey checklist

Seven things to record before you hand a fire load figure to an officer or a consultant.

The floor area of each compartment surveyed, in m² BIS, SP 7:2026
The mass of each combustible, grouped by material IS 1641:1988
The building's combustible parts: partitions, false ceilings, floor and wall finishes IS 1641:1988
The Table 12 calorific value used for each material, with its serial number BIS, SP 7:2026
A separate figure for each concentrated stack or store IS 1641:1988
The processes carried on and the interior finishes, which can raise the class BIS, SP 7:2026
For industry, the Annex B class you think applies: G1, G2 or G3 BIS, SP 7:2026

What Flamekite could not confirm about fire load

Five gaps, stated so no one mistakes a blog figure for a code figure.

The low, moderate and high bands quoted online, under 2,75,000 kcal/m², 2,75,000 to 5,50,000 and above, are attributed to IS 1641. They are not in its 1988 text, and Flamekite did not find the edition they come from.

IS 1641:2013, the current edition, has not been read by Flamekite. IS 15105:2021, whose light, ordinary and high hazard groups Mizoram's 2026 rules adopt, has been read and is summarised on its own page. The BIS database shows IS 15105:2021 as current although its listed validity date, 31 March 2026, has passed.

Table 7K prints a sprinkler demand pair for each level, such as 12.2 and 230 for CL-5, without units. Flamekite does not convert them.

Part F does not map a fire load density to a protection level: there is no line saying a given MJ/m² means CL-4. The authority makes that judgement, which is why the decision section above names who decides.

The 2018 survey figures come from a news report of a Current Science paper; the paper's own page did not load, so its exact numbers were not checked against the original.

Fire load questions people ask

What is fire load?: Fire load is the total heat the contents of a room, floor or building could release if they all burned, measured in megajoules. NBCS 2026 Part F defines it in clause 2.25, and IS 1641 also counts the building's own combustible parts.
What is fire load density?: Fire load density is the fire load divided by the floor area, in MJ/m² or in kg of wood equivalent per m². Part F gives typical values: about 25 kg/m² for homes, 25 to 50 for offices and up to 500 for storage.
What is the formula for fire load calculation?: Multiply the mass of each combustible material by its calorific value, add the results, and divide by the floor area. A 20 m² office with 400 kg of wood at 17.6 MJ/kg has 7,040 MJ from the wood alone, or 352 MJ/m².
What is the unit of fire load?: Megajoules (MJ) for fire load and MJ/m² for fire load density in NBCS 2026. The older IS 1641:1988 used kilocalories per m². Part F also expresses density as kg of wood equivalent per m².
What calorific value of wood should I use?: 17.6 MJ/kg, the value in NBCS 2026 Part F Annex A, Table 12, for hard or soft wood. It is also the 1.00 on the wood-equivalent scale the table uses for every other material.
Which IS code covers fire load?: IS 1641, on fire grading and classification; the current edition is IS 1641:2013. NBCS 2026 Part F carries the working definitions, the density table and the calorific values in Annex A.
What is the fire load density of an office?: Part F puts business buildings at 25 to 50 kg of wood equivalent per m², about 440 to 880 MJ/m². A 2018 survey of offices and dormitories in Ahmedabad reported about 1,400 MJ/m² on average.
What is the difference between fire load and occupant load?: Fire load is the energy stored in what can burn. Occupant load is the number of people a floor is designed for, used to size exits. Both appear in Part F, but they size different things.

Keep reading

Fire safety glossaryEvery fire-law term, defined from the act, rule or code that uses it.
Wet riserThe pipe the hazard class and the pump size end up feeding.
National Building Code 2026Part F, the occupancy groups and which edition your state uses.
Fire NOC in AssamSchedule I vulnerability classes and the fines they set.
Fire NOC in TripuraThe 2026 rules that define fire load in state law.
Fire NOC in MizoramCommon NOCs for industrial estates and sprinkler spacing by hazard.
Fire NOC checkerCheck whether your building needs a fire NOC in your state.

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Fire load at a glance

Fire load in IS 1641:1988 and NBCS 2026

How to calculate fire load, step by step

Mark the compartment and its floor area

List every combustible by material

Take each calorific value from Table 12

Multiply and add

Divide by the floor area

Check concentrations separately

Hand it to the authority with the processes