Flow & Pressures

Flow Rate

MMSCFD

At 14.696 psia and 60°F standard conditions

Suction Pressure

psig

Inlet pressure (gauge)

Discharge Pressure

psig

Outlet pressure (gauge)

Tip: Compression ratio r = P₂/P₁. Keep r < 4 per stage for centrifugal, < 6 for reciprocating to limit discharge temperature.

Gas Properties

Gas Type Selects k-value and molecular weight

Specific Heat Ratio (k = Cₚ/Cᵥ)

—

Per GPSA Fig. 13-4; k decreases with temperature

Molecular Weight (MW)

lb/lbmol

For natural gas: MW ≈ 28.97 × SG

Inlet Temperature

°F

Performance Parameters

Calculation Method

Isentropic — Adiabatic per GPSA; use for reciprocating Polytropic — Per API 617; use for centrifugal

Isentropic (adiabatic) per GPSA; use for reciprocating

Efficiency (η)

—

Isentropic efficiency: 0.70–0.85 typical

Compressibility Factor (Z)

—

Average of suction and discharge; use 0.85–1.0

Include Motor Sizing Size motor with NEMA service factor

Service Factor

—

NEMA standard: 1.15 for continuous duty

Note: η_polytropic > η_isentropic for same machine. For centrifugal: use polytropic per API 617. For recip: use isentropic.

Quick Reference: Typical k-Values & Efficiencies

Gas	k @ 60°F	MW	Compressor Type	η Range
Natural Gas	1.27	18.9	Centrifugal	0.75–0.82 (poly)
Methane	1.31	16.04	Reciprocating	0.80–0.88 (isen)
Ethane	1.19	30.07	Screw	0.70–0.80 (isen)
Propane	1.13	44.10	Axial	0.82–0.88 (poly)
CO₂	1.29	44.01	Use Z < 0.9 near critical

📚 Learn the Theory

Detailed coverage of adiabatic, polytropic, and isothermal compression with efficiency factors per API 617.

Read Engineering Guide →

Horsepower Results

Brake Horsepower

—

Gas Horsepower —

Compression Ratio —

Discharge Temperature —

ACFM @ Suction —

Head —

Mass Flow —

Formula (GPSA Method)

                                Isentropic Head:

                                H = (Z·R·T₁/MW)·(k/(k-1))·[(P₂/P₁)^((k-1)/k) - 1]
                                
                                Brake HP:

                                BHP = (ṁ · H) / (33,000 · η)
                                
                                Discharge Temp:

                                T₂ = T₁ + (T₂ₛ - T₁)/η

                                where T₂ₛ = T₁·(P₂/P₁)^((k-1)/k)

H = Head (ft·lbf/lb)

Z = Compressibility factor

R = 1545 ft·lbf/(lbmol·°R)

T₁ = Suction temp (°R)

ṁ = Mass flow (lb/min)

η = Efficiency (decimal)

Standards & References

GPSA
13th/14th Edition, Section 13
API 617
Axial and Centrifugal Compressors
API 618
Reciprocating Compressors
ASME PTC-10
Compressor Performance Test Code

Compressor Horsepower Calculator

Flow & Pressures

Gas Properties

Performance Parameters

Quick Reference: Typical k-Values & Efficiencies

📚 Learn the Theory

Horsepower Results

Motor Sizing

Staging Analysis

Recommendations

Formula (GPSA Method)

Standards & References

Compressor Horsepower Calculator

Flow & Pressures

Gas Properties

Performance Parameters

Quick Reference: Typical k-Values & Efficiencies

📚 Learn the Theory

Horsepower Results

Motor Sizing

Staging Analysis

Recommendations

Formula (GPSA Method)

Standards & References

Related Calculators

Gas Density

Pipeline Hydraulics

Line Sizing

Pipe Volume