NFPA in USA

NFPA 25 calculator

Available Water Supply Calculator

Estimate available flow at a required residual pressure from a hydrant flow test.

Water Supply AnalysisNFPA 25Workpaper

Calculation workpaper

Enter inputs, review outputs, then use the guidance below before carrying the result forward.

US customary units

Calculation inputs

Enter project screening values in the units shown.

Ready

Worksheet header

Optional project fields for keeping the calculation screen traceable.

Results

Ready

Available flow

1,809.9 GPM

Calculated output

Available flow1,809.9GPM

NFPA in USA calculation workpaper

Available Water Supply Calculator

NFPA 25 ยท Water Supply Analysis

nfpainusa.comGenerated record

Project record

Project ID
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Area
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System
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Revision
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Prepared by
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Checked by
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Inputs

Measured test flow
1000 GPM
Static pressure
80 psi
Residual pressure
60 psi
Required residual
20 psi

Results

Available flow
1,809.9 GPM

Calculation basis

Formula
Qavail = Qtest x ((Ps - Preq) / (Ps - Pr))^0.54
Reference standard
NFPA 25
Professional boundary
Verify adopted code, project criteria, listed equipment data, and AHJ requirements before relying on this record.
NFPA in USAnfpainusa.comThis is a calculation record, not a signed or sealed engineering document.

Calculation basis

Use the formula and linked reference data after the result is visible. Keep input selection separate from the calculation screen.

Formula

Qavail = Qtest x ((Ps - Preq) / (Ps - Pr))^0.54

Review note

Confirm units before comparing results. If the value controls a design choice, check it against adopted criteria and project-specific inputs.

Use this result

Use available flow at required residual for demand comparison.

Check before use
Confirm static, residual, test flow, and required residual pressures are from the same test basis.
Common pitfall
Comparing demand at a different residual pressure basis can misstate water supply margin.
Next step
Sprinkler System Demand Calculator

Input evidence

Confirm these values before using the result.

  • Measured test flow (GPM)
  • Static pressure (psi)
  • Residual pressure (psi)
  • Required residual (psi)

Authority basis

Check jurisdiction, AHJ, submittal, and edition records before using this result as project evidence.

AHJ Contact ChecklistInspection and Testing Forms WorkflowNFPA 13, 72, and 25 Edition Basis Worksheet

Record retention

Save the PDF after project fields, inputs, and results are set.

PDF includes

  • Project header and calculator inputs
  • Computed result rows and warnings
  • Formula, reference basis, and professional boundary

Check before filing

  • Input traceability
  • Method review
  • Output reasonableness
  • Professional boundary

Open next

Hydrant Flow and Water Supply WorksheetSprinkler Pipe Internal Diameter ReferenceNFPA 25 Flow Test and Water Supply Calculators
Engineering disclaimer
NFPA in USA provides engineering workpapers, calculation checks, and reference tables for project screening and coordination. Final design decisions, code interpretations, submittals, and acceptance records must be completed by qualified professionals and verified against the adopted code, project criteria, listings, and Authority Having Jurisdiction requirements. This site does not issue signed or sealed engineering documents.

Related tools and tables

Hydrant Flow Test CalculatorNFPA 25 tool hub

FAQ

What is this Available Water Supply calculator for?+
Use it to compute a defined fire protection value from documented inputs, then retain the inputs, result, formula, and warnings with the project record.
Are the results suitable for permit submission?+
Use the saved record only after it is checked against adopted code, project criteria, equipment listings, and AHJ requirements.