How much refrigerant do you add per foot of line set?

It depends on the liquid line diameter. Common figures are about 0.27 oz/ft for 1/4" line, 0.40 oz/ft for 5/16", and 0.60 oz/ft for 3/8". You only add for liquid line length beyond what the factory charge already covers, and the manufacturer's published value always governs.

Do you add charge for the suction (vapor) line?

Generally no. The liquid line holds the vast majority of the additional refrigerant mass; the vapor line contains comparatively little. Most residential charge-adjustment tables are based on liquid line length only — but check the manufacturer's instructions, as some equipment specifies otherwise.

How long is a factory line-set charge good for?

Most split systems ship pre-charged for a baseline line length, commonly 15 to 25 feet. Beyond that baseline you add refrigerant per foot; below it some manufacturers have you remove a small amount. Always use the value on the data tag or in the install manual.

Is the calculated line charge exact?

No — treat it as a starting estimate. The per-foot figures are industry standards, but refrigerant type, ambient conditions, and the specific equipment all matter. Always confirm the final charge with the subcooling method (TXV systems) or superheat (fixed-orifice systems).

Line-Set Charge Calculator

Free refrigerant line-set charge calculator. Estimate the extra refrigerant to add per foot of liquid line beyond the factory-charged length, by liquid line diameter.

How the line-set charge calculation works

A split system ships pre-charged for a baseline liquid line length (commonly 15–25 ft). When the installed run is longer, you add refrigerant for the extra liquid line — and almost all of that added mass lives in the liquid line, so the adjustment is based on liquid line diameter:

Additional charge (oz) = oz-per-foot × (total liquid line length − factory-charged length)

Liquid line OD	Typical charge rate
1/4”	~0.27 oz/ft
5/16”	~0.40 oz/ft
3/8”	~0.60 oz/ft

Worked example

A system with a 3/8” liquid line has a 45 ft run and a factory baseline of 15 ft:

0.60 oz/ft × (45 − 15) = 0.60 × 30 = 18 oz (1 lb 2 oz) of refrigerant to add.

Important cautions

The manufacturer’s charge table governs. Different equipment and refrigerants (R-410A, R-454B, R-22) can specify different per-foot values — always use the data tag or install manual when available.
This is a starting estimate, not the final charge. Confirm the actual charge by subcooling on a TXV system or by target superheat on a fixed-orifice system.
The adjustment is for liquid line length; most residential tables omit the vapor line, but check the manufacturer’s instructions for your unit.

How FieldPad helps in the field

Estimate the line-set charge here, then record the actual charge in FieldPad against the equipment and the install job. Log the line length, the refrigerant, and the final verified charge on one record, and roll it straight into the install invoice — offline, on your iPhone.

Line-Set Charge Calculator

How the line-set charge calculation works

Worked example

Important cautions

How FieldPad helps in the field

Stop Re-Running These Numbers by Hand

Related Tools

Compression Ratio Calculator

Refrigerant PT Chart Calculator

Subcooling Calculator

Superheat Calculator

Target Superheat Calculator (Fixed Orifice)