Coverage Area by 2X Throw, or the Actual Area?

2/2/2026

I am attempting to tweak a set of calculations that is slightly over the curve.

When measuring/assigning an area of coverage for an individual sprinkler into a hydraulic calculation program I am told the area per sprinkler is the largest dimension x 2, not the physical area the sprinkler protects. This is because the required distribution of water will be based on the largest dimension regardless of the physical dimensions of area protected.

Comparison example:

1) Physical Area for Pendent Sprinkler coverage is 14 x 8 = 112 sqft
Flow determined by 112 sq ft x .10 gpm = 11.2 gpm

2) Largest Dimension x 2 determines area per sprinkler and area is 14 x 14 = 196 sqft
Flow determined by 196 sq ft x .10 gpm = 19.6 gpm

Thanks in advance for your opinion and code basis.

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5 Comments

Dan Wilder

2/2/2026 07:52:53 am

Unless your sprinklers are residential, extended coverage, CMSA (sometimes) or ESFR, the SxL method is the correct approach.

One clarification, the SxL are two different calculated numbers for SSU/SSP. To find either, it is the greater number of:
The total distance between 2 sprinklers
The distance to a wall (sometimes obstructions) x2

Repeat for the branch line calculation. You would not just take the largest of the SxL and apply that to the second number.

For SSU/SSP
2019-13
10.2.5 for spacing requirements
19.3.3 for density requirements
Specific to your question - 27.4.2.6.2
27.2.4.7.1 for discharge requirements

2/2/2026 08:26:44 am

There is nothing in NFPA 13 that limits the square footage used in CMDA hydraulic calculations, however contract documents, AHJ requirements, insurance requirements may dictate maximum allowable spacing be used for future modifications. If you use a smaller area than the maximum, make sure it's clearly indicated on the drawings and calculations, noted on the hydraulic placard/general information sign, and that the spacing throughout the building matches the spacing of the sprinklers in the remote area that you proved hydraulically (you can't calc to 196ft and space 225ft everywhere else without additional calculations).

2/2/2026 11:20:23 am

Definitely the largest of x2 dimension is what determines the area per sprinkler (so in your comparison example the coverage area is 196sqft not 112sq ft). I won't repeat good points already stated; however wanted to add one. If you have a OH occupancy, based upon the example you gave, you would end up with two heads in that small compartment vs one as the coverage area exceeds 130sqft.

Comparison example:

1) Physical Area for Pendent Sprinkler coverage is 14 x 8 = 112 sqft
Flow determined by 112 sq ft x .10 gpm = 11.2 gpm

2) Largest Dimension x 2 determines area per sprinkler and area is 14 x 14 = 196 sqft
Flow determined by 196 sq ft x .10 gpm = 19.6 gpm

Wes

2/2/2026 11:40:48 am

DG, in your 14 x 8 example, where does this requirement originate?

In concept, I understand that throwing 7-ft in either direction to cover 14 foot, with a sprinkler that deflects in a conical pattern, logically would be 14 x 14 ft; but what's the standard or code basis to doing so?

Technically (I wouldn't) someone could say that in order to throw 7-ft to one side, you can achieve that with an equivalent area (round circle) of 153.9 sqft (pi * 7-ft ^2). No one does that, but if we're making an argument that the THROW of the sprinkler needs to be accommodated so we're taking the larger distance twice (14 x 14), that's also a mathematical equivalent.

If a sprinkler covers 112 sqft actual or 112 S x L sqft calculated, what requires us to calculate an area of 196 sqft for a density?

I may have missed it, but I'm not familiar with a section of NFPA 13 that spells out the longest-throw distance and squares it for the density calculation.

Brett

2/2/2026 02:19:08 pm

Wes, the general spacing rules are in section 9.5.2.1 in the 2019 edition of NFPA 13. Dan pointed out the other applicable sections above (although there is a typo - 27.4.2.6.2 should be 27.2.4.6.2) and the fact that some sprinkler types have different spacing rules that override 9.5.2.1.

One thing I will add is that if the sprinklers you're calculating are in a small room (which has a definition in chapter 3) then the coverage area of those sprinklers is the area of the room divided by the number of sprinklers. That's in section 10.2.4.1.2.1 in NFPA 13 2019 edition.

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Coverage Area by 2X Throw, or the Actual Area?

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