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How to calculate superheat

Last updated: October 17, 2026

Superheat tells you how far the refrigerant vapor has warmed above its saturation temperature. Here is the calculation, step by step.

What superheat is

Superheat is the number of degrees the refrigerant vapor is above the temperature at which it would boil (its saturation temperature) at the same pressure. It is measured on the low side, at the suction line, and it shows whether vapor leaving the evaporator is fully vaporized.

The formula

Superheat = suction line temperature − saturation temperature at suction pressure

For a blend with temperature glide, use the dew point (saturated vapor) column for the saturation temperature. See bubble point versus dew point.

Step by step

  1. Let the system run and stabilize, and confirm airflow is normal before you read anything.
  2. Read suction pressure at the suction service port, in gauge pressure.
  3. Look up the saturation temperature for that pressure for the refrigerant in the system, using the dew-point value.
  4. Measure the suction line temperature with a pipe clamp or probe, at the location your equipment manufacturer specifies, with good contact and insulation over the probe.
  5. Subtract: line temperature minus saturation temperature is the superheat.

Worked example

R-410A, suction pressure 118 psig. The dew-point saturation temperature at 118 psig is about 39.8 °F in the P-T data bundled in HVAC Charge Pro. The measured suction line temperature is 50.0 °F.

50.0 °F − 39.8 °F = 10.2 °F superheat

The inputs are illustrative. The result says nothing about whether this system is correctly charged until you compare it with the right target.

What the number is compared with

There is no single correct superheat for every system. On fixed-metering systems (such as a piston or cap tube) the target is usually taken from the manufacturer’s charging chart or the equipment label, typically using indoor wet-bulb and outdoor dry-bulb temperatures. On TXV and EEV systems the valve regulates superheat, and the charge is generally verified by subcooling against the manufacturer’s target.

HVAC Charge Pro calculates the actual superheat from your readings. It does not supply a target superheat, so keep the manufacturer’s data handy.

Before you trust a reading

  • Airflow: dirty filters, blocked coils and weak blowers can mimic a charge problem.
  • Instruments: confirm gauge and probe accuracy and that the refrigerant selected matches the system.
  • Stability: wait for pressures and temperatures to settle.
  • Units: gauge pressure, not absolute, and the same temperature unit throughout.

Further reading

HVAC School explains how technicians find target superheat: How to find target superheat ↗. This is an independent third-party resource and is not affiliated with HVAC Charge Pro.

HVAC Charge Pro and this guide are calculation and reference aids. A superheat or subcooling value alone does not decide whether to add or remove refrigerant. Follow the equipment manufacturer’s instructions, approved service procedures and applicable safety requirements.

Read the Engineering Disclaimer ↗