TradeToolsHVAC · in the TradeTools app
Line-Set Charge Calculator
How much refrigerant the copper lines themselves hold, for the length beyond what the nameplate charge already covers — liquid line and suction line, in ounces, pounds and grams, for ten refrigerants.
Copper ACR line volumes · per-foot charge
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Worked example
50 ft line set on an R-410A split, nameplate charge good for 15 ft — how much to add?
| Refrigerant | R-410A |
|---|---|
| Liquid line length | 35 ft (50 − 15) |
| Liquid line size | 3/8" |
| Suction line length | 35 ft |
| Suction line size | 3/4" |
| Total line-set charge | 23.3 oz |
|---|---|
| Total line-set charge | 1.45 lb |
| Liquid line | 20.3 oz |
| Suction line | 3.0 oz |
3/8 in ACR tube has a 0.315 in bore — 0.935 in³ per foot — and R-410A saturated liquid at 70 °F is 1078 kg/m³, so each foot holds 0.58 oz: 35 ft, 20.3 oz. The 3/4 in suction line carries vapor at about 35 kg/m³, 0.085 oz per foot: 3.0 oz. Together 23.3 oz, 1.45 lb, 660 g. Manufacturer long-line guides publish about 0.6 oz per foot for 3/8 in liquid line, which 0.58 rounds to.
How it's calculated
The table behind the number
Ounces per foot is the inside cross-section of the copper ACR tube, times 12 inches, times the refrigerant density — saturated liquid at 70 °F for the liquid line (an equalized, off-cycle line), saturated vapor at 40 °F for the suction line. The app multiplies each by its length and adds the two. Enter only the length beyond what the factory charge covers, and use the per-foot value from the installation manual when it gives one: some manufacturers publish a figure for their own line sizes and conditions.
- Copper ACR tubeInside diameter by nominal size: 1/4 in 0.190, 3/8 in 0.315, 1/2 in 0.430, 3/4 in 0.666, 7/8 in 0.785
- Refrigerant propertiesSaturated liquid density at 70 °F and saturated vapor density at 40 °F from reference equations of state (NIST REFPROP-grade, via CoolProp)
- Manufacturer long-line guidesPublished per-foot additions — about 0.6 oz per foot for 3/8 in liquid line on R-410A and R-454B systems
Questions
Before you trust the number
Do I enter the whole line set or just the extra?
Just the extra. A nameplate charge is figured for a stated line length — the installation manual gives it; 15 ft in the example above — so enter the run beyond that. Enter the whole length only when the manufacturer's charge covers none of the line.
Why so little for the suction line?
Because it carries vapor. R-410A vapor at 40 °F is about 35 kg/m³ against 1078 for liquid at 70 °F, so a 3/4 in suction line holds 0.085 oz per foot — about a seventh of what the 3/8 in liquid line holds, despite twice the diameter.
Is the number final?
It is the starting weight. Weigh the charge in, then verify by subcooling on a TXV system or superheat on a fixed orifice against the unit's charging chart at running conditions — that check catches a mis-measured line, a different tube size or refrigerant left in the lines.