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Compressor Capacity Calculator

Work out compressor capacity instantly with clear inputs, formula shown and shareable results.

About Compressor Capacity Calculator

Compressor capacity is mass flow multiplied by the net refrigerating effect, the enthalpy the refrigerant gains crossing the evaporator. Because a ton of refrigeration is 12,000 BTU/h, dividing gives nominal tonnage, and mass flow per ton is a quick sanity check against published compressor data.

Formulas

Capacity

Q = mass flow x (h1 - h4)

h1
Enthalpy leaving evaporator
h4
Enthalpy entering evaporator

Tonnage

tons = Q / 12000

Worked example

With the default values below, Compressor Capacity Calculator returns Refrigeration capacity of 20,400. Change any input above and every figure here is recalculated in your browser.

Inputs used

Refrigerant mass flowminimum 1 lb/h
300 lb/h
Enthalpy leaving evaporatorminimum 1 BTU/lb
108 BTU/lb
Enthalpy entering evaporatorminimum 0 BTU/lb
40 BTU/lb

Results

Refrigeration capacity
20,400 BTU/h
Capacity in tons
1.70 tons
Net refrigerating effect
68.0 BTU/lb
Mass flow per ton
176.47 lb/h/ton

Step by step

  1. 1Values used
  2. 2Capacity
  3. 3Tonnage
  4. 4Refrigeration capacity= 20,400 BTU/h
  5. 5Capacity in tons= 1.70 tons
  6. 6Net refrigerating effect= 68.0 BTU/lb
  7. 7Mass flow per ton= 176.47 lb/h/ton

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Compressor Capacity figure worked out?

Q = mass flow x (h1 - h4). Compressor capacity is mass flow multiplied by the net refrigerating effect, the enthalpy the refrigerant gains crossing the evaporator.

Why does capacity fall in hot weather?

A higher condensing temperature raises the enthalpy of the liquid entering the evaporator, shrinking the net refrigerating effect while also cutting volumetric efficiency.

What values do I need to enter?

This calculator takes 3 inputs: Refrigerant mass flow, Enthalpy leaving evaporator, Enthalpy entering evaporator. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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