NFPA in USA

Engineering calculator

NPSH Calculator

Screen net positive suction head conditions for fire pump suction arrangement review.

Fire PumpEngineeringWorkpaper

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

NPSH available

44.9 ft

Calculated output

Required NPSH

10 ft

Calculated output

NPSH margin

34.9 ft

Calculated output

NPSH available44.9ft
Required NPSH10ft
NPSH margin34.9ft
NPSH screenPass

Before project use

Save the input source, formula, units, warnings, and result with the project record before carrying this screening value into design coordination or AHJ review.

Next calculator: Fire Pump Rated Flow and Pressure Calculator

NFPA in USA calculation workpaper

NPSH Calculator

Engineering ยท Fire Pump

nfpainusa.comGenerated record

Project record

Project ID
Not entered
Area
Not entered
System
Not entered
Revision
Not entered
Prepared by
Not entered
Checked by
Not entered

Inputs

Suction head
18 ft
Atmospheric head
33.9 ft
Suction friction loss
6 ft
Vapor pressure head
1 ft
Required NPSH
10 ft

Results

NPSH available
44.9 ft
Required NPSH
10 ft
NPSH margin
34.9 ft
NPSH screen
Pass

Calculation basis

Formula
NPSH available = suction head - vapor and friction losses
Reference standard
Engineering
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

NPSH available = suction head - vapor and friction losses

Nominal Pipe Diameter

Nominal SizeSchedule 10 ID (in)Schedule 40 ID (in)
3/4"0.8840.824
1"1.0971.049
1-1/4"1.4421.38
1-1/2"1.6821.61
2"2.1572.067
2-1/2"2.6352.469

Professional review path

Use this calculator as a workpaper step: collect evidence, make a review decision, then move the record into the next workflow.

Evidence to collect
  • Suction head and atmospheric head basis for the pump location.
  • Suction friction loss and vapor pressure head assumptions used in the screen.
  • Required NPSH value from manufacturer data or pump selection basis.
Review decision
Decide whether the NPSH margin supports the pump arrangement or requires suction redesign/manufacturer review.

Use this result

Use NPSH margin to flag suction conditions that need deeper pump review.

Check before use
Confirm suction head, atmospheric head, friction loss, vapor head, and required NPSH.
Common pitfall
A positive discharge pressure screen does not prove acceptable suction conditions.
Next step
Fire Pump Sizing Calculator

Input evidence

Confirm these values before using the result.

  • Suction head (ft)
  • Atmospheric head (ft)
  • Suction friction loss (ft)
  • Vapor pressure head (ft)
  • Required NPSH (ft)

Authority basis

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

State and Local Code Adoption WorkflowAHJ Contact ChecklistFire Protection Submittal ChecklistNFPA 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

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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

Fire Pump Sizing CalculatorFire Pump Selection WorksheetSprinkler Pipe Internal Diameter Reference

FAQ

What is this NPSH 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.