Compression Ratio Calculator
Free compression ratio calculator for HVAC/R techs. Enter discharge and suction pressures to get the absolute compression ratio, with healthy-range guidance and what a high ratio means.
How the compression ratio calculation works
Compression ratio is how many times the compressor multiplies the absolute pressure of the refrigerant from the suction side to the discharge side. It’s a quick gauge of how hard the compressor is working:
Compression Ratio = (Discharge PSIG + 14.7) ÷ (Suction PSIG + 14.7)
You must convert gauge pressure to absolute pressure first. Gauges read 0 at atmospheric pressure, but the compressor sees true absolute pressure, so you add 14.7 PSI (sea-level atmospheric) to each reading before dividing. At higher altitude, atmospheric pressure is lower — drop the constant accordingly for a more precise number.
Worked example
A system reads 260 PSIG discharge and 70 PSIG suction:
(260 + 14.7) ÷ (70 + 14.7) = 274.7 ÷ 84.7 ≈ 3.24 : 1
That’s a healthy ratio.
Reading the result
| Ratio | Meaning |
|---|---|
| ~2.3 : 1 – 3.5 : 1 | Typical, healthy operating range |
| 3.5 : 1 – 4 : 1 | Elevated — investigate condenser, charge, suction |
| Over 4 : 1 | Mechanical/thermal stress; amp draw climbs 15–25%; risk of valve and bearing wear |
A high ratio is driven by low suction (undercharge, restriction, low load, poor evaporator heat transfer), high discharge (dirty condenser, dead condenser fan, overcharge, non-condensables), or both. The ratio tells you something is wrong — read the high-side and low-side pressures individually to find what.
Never add refrigerant just because the ratio is high. Confirm the root cause first — pair this with superheat and subcooling, and use the PT chart to convert pressures to saturation temperatures.
How FieldPad helps in the field
Run the ratio here, then keep the diagnosis where the job lives. FieldPad logs your pressure readings and findings against the equipment and the client, attaches them to the service job, and turns the repair into a signed estimate or invoice — offline, on your iPhone, with the full history on one record.
Stop Re-Running These Numbers by Hand
FieldPad is the all-in-one iPhone CRM for solo HVAC techs — clients, scheduling, estimates, invoices with signatures, inventory, and equipment history. Keep your readings on the job, the client, and the equipment, all in one offline-ready app. EPA Section 608 and Subpart C compliance included.
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