SizingKitLine set
Refrigerant charge calculator
A condensing unit leaves the factory holding enough refrigerant for a line set of a stated length, and this free page works out the weight to add or take away when the one you ran is a different length. Give it the liquid line size, the run and the allowance off the data plate and it returns the correction in ounces, in pounds and ounces, and in grams, from the tube's own bore and the saturated liquid density. No gauges are involved and the system does not need to be running — it is arithmetic you can do before the vacuum pump comes off.
- 100% free
- No signup
- 8 ACR sizes
- Ounces and grams
- Factory length editable
The line set as installed
Measure the run, read the factory allowance off the data plate, and the difference between them is a weight. Nothing here needs the system to be running, or even brazed.
Changing this reloads the density below with that refrigerant’s own 77 °F figure.
0.311 in inside (7.9 mm), from a 0.032 in wall. ACR tube is named by its outside diameter, so a 3/8 in line really does measure 3/8 in across.
The tube you actually ran, vertical rise included. Feet unless you write a unit: 47 ft 6 in and 15 m both read.
Default 15 ft — The line-set length most residential condensing units are factory-charged for; charge is added or removed for the difference. Manufacturer-dependent — 25 ft is also common, and some units are charged for the outdoor unit alone with the whole line set and indoor coil to be added. It is printed on the unit's data plate, and getting it wrong puts the charge out by the whole factory allowance.
Default 66.2 lb/ft³ — Saturated liquid density at 77 °F (25 °C), 1060 kg/m³. Falls steeply with temperature — roughly 8% lower at 120 °F. Line-set charge computed from volume moves with it, which is one reason manufacturers publish a flat figure per foot rather than an equation.
Fill this in and the plate below adds the adjustment to it, so the scale has one number to reach rather than two.
Line-set charge adjustment
ADD — OUNCES
19.6 oz
ADD — GRAMS
554 g
- As a scale reads it
- 1 lb 3.6 oz
- This line holds
- 0.559 oz/ft / 52 g/m
- Total with nameplate
- —
35 ft of liquid line past the allowance is what decides this. 50 ft installed, 15 ft already in the unit, 0.311 in bore holding 0.559 oz of liquid per foot. Read the factory allowance off the wrong plate and the answer is out by the whole of it: 8.4 oz on this size at the 15 ft set above.
Volume comes from ASTM B280 seamless copper tube for air conditioning and refrigeration field service, hard-drawn: nominal size is the outside diameter, and the wall thicknesses listed are the ordinary ACR walls for each size. Annealed (soft) coils of the same nominal size can carry a different wall, and line sets sold as an assembly state their own. Which size goes where is a design decision from the equipment's own line-sizing tables — it depends on the capacity, the length, the lift and the oil return, and a suction line that is too large fails to carry oil back to the compressor even though it flows perfectly well. The weight is that volume multiplied by the saturated liquid density in the field above, which is why the figures here run slightly under a manufacturer’s published ounces per foot: the published table is computed at a colder, denser liquid and rounded upward, and the warranty is written against the published table rather than against this arithmetic. Where the two disagree, weigh in to theirs.
Refrigerant per foot of ACR tube
Every size a residential line set is made from, full of saturated liquid at 77 °F. Suction rows are here to show why they are excluded, not to be added: a vapor line of the same bore holds a small fraction of the weight printed against it.
| OD | ID in / mm | Usually | R-410A oz/ft (g/m) | R-22 oz/ft (g/m) | R-134a oz/ft (g/m) |
|---|---|---|---|---|---|
| 1/4 | 0.19 / 4.83 | liquid | 0.209 (19) | 0.234 (22) | 0.237 (22) |
| 5/16 | 0.249 / 6.31 | liquid | 0.357 (33) | 0.401 (37) | 0.406 (38) |
| 3/8 | 0.311 / 7.9 | liquid | 0.559 (52) | 0.628 (58) | 0.636 (59) |
| 1/2 | 0.436 / 11.07 | either | 1.098 (102) | 1.234 (115) | 1.249 (116) |
| 5/8 | 0.555 / 14.1 | suction | 1.779 (166) | 2 (186) | 2.024 (188) |
| 3/4 | 0.68 / 17.27 | suction | 2.671 (248) | 3.002 (279) | 3.039 (283) |
| 7/8 | 0.785 / 19.94 | suction | 3.56 (331) | 4.001 (372) | 4.049 (377) |
| 1 1/8 | 1.025 / 26.04 | suction | 6.07 (565) | 6.821 (634) | 6.904 (642) |
Densities used: R-410A 66.2 lb/ft³, R-22 74.4 lb/ft³, R-134a 75.3 lb/ft³. The plate above uses the density in your own field instead, so an edited figure moves the answer without moving this reference table.
How to work out a line-set charge adjustment
Three inputs, and the one people get wrong is not the length.
Read the factory allowance off the data plate
The plate on the outdoor unit states the charge and the line-set length that charge covers. Fifteen feet is the commonest, twenty-five is not unusual, and some units ship charged for the outdoor section alone with the whole line set and the indoor coil still to be added. Type what yours says into the allowance field rather than accepting the default, because getting this figure wrong moves the answer by the entire allowance — on a 3/8 in liquid line a 15 ft allowance is 8.4 oz of R-410A, before you have measured a thing.
Measure the liquid line, not the pair
The correction is computed from the small line only. Measure the tube as installed, including the vertical rise and the loops at each end, and enter it in feet or in meters — 47 ft 6 in and 15 m both read. Then pick the nominal size: ACR tube is named by its outside diameter, so a 3/8 in liquid line genuinely measures 3/8 in across the outside, unlike the water tube in the same building. The page derives the bore from the wall thickness rather than looking up a published inside diameter.
Weigh it in, then verify with the gauges
Add the nameplate charge and the adjustment together, put the cylinder on a scale and charge to that total on a system you have evacuated. The scale is the accurate instrument here; the manifold is not. Once the machine has run and settled, confirm the result on whichever side of the system its metering device makes meaningful — the liquid side on a valve, the suction side on a piston — and treat a disagreement as a question about the equipment rather than as a license to keep adding.
Technical specifications
| Line sizes | Eight ASTM B280 ACR sizes from 1/4 to 1 1/8 in outside diameter. Inside diameter and internal volume are computed from the wall thickness, so no diameter on this page has been transcribed from anywhere. |
|---|---|
| Liquid line capacity | A 3/8 in ACR line holds 0.559 oz/ft of R-410A, 0.628 oz/ft of R-22 and 0.636 oz/ft of R-134a at their 77 °F saturated liquid densities. |
| Factory allowance | 15 ft prefilled and editable. 25 ft is also common, and a unit charged for the outdoor section alone is legitimately entered as 0. |
| Worked example | 50 ft of 3/8 in liquid line on R-410A against a 15 ft allowance: add 19.6 oz, which a scale shows as 1 lb 3.6 oz and a metric scale as 554 g. |
| Suction line | Excluded from the arithmetic. The reference table prints what each size would hold full of liquid; a vapor line of the same bore carries a small fraction of that, which is why manufacturers write the adjustment against the liquid line alone. |
| Liquid density | 66.2 lb/ft³ for R-410A at 77 °F, prefilled and editable. It falls roughly 8% by 120 °F, which is why a manufacturer publishes a flat ounces-per-foot figure rather than an equation. |
| Output units | Ounces, pounds and ounces, grams and kilograms, with grams per meter alongside ounces per foot on the reference table. |
| Where the job numbers stay | In the browser. The run length, the nameplate charge and the equipment you are working on are not transmitted or stored anywhere. |
Frequently asked questions
Is this the whole charge or only the adjustment?
It is the adjustment by default, and it becomes the total if you fill in the optional nameplate field. The number the plate states is the charge for the unit plus its stated line-set allowance, so a complete charge for a real installation is that figure plus what this page returns. Entering the nameplate weight makes the tool add the two together and print a single target, which is the number to charge the scale to rather than doing the addition on the roof.
Why does the suction line not count?
Because it is full of vapor, and vapor of the same volume weighs a small fraction of what liquid does. The correction is a mass of refrigerant, and mass is volume times density; the liquid line is the only part of the set holding a fluid dense enough for its length to matter. Every manufacturer's adjustment table is written against the liquid line size for the same reason, so adding a suction-line contribution on top of one of those tables double-counts something that was never in them.
My line set is shorter than 15 ft. Do I really take refrigerant out?
Arithmetically yes, and in practice most installers on a residential split do not. The tool shows the negative figure because it is the honest answer and because it is worth knowing how big it is: a 3/8 in line set ten feet short of the allowance is about five and a half ounces of R-410A, which on a small system is a real fraction of the charge. Recovering that much out of a factory-sealed unit is fiddly, so treat it as a decision to make deliberately and then confirm the result on the appropriate side of the system rather than as something to ignore by default.
The plate says the unit is charged for 25 ft, not 15. What do I change?
Type 25 into the allowance field and nothing else. The default is a common value rather than a standard, and the plate always wins — that is why the field is editable and why it prints where the default came from underneath. It also means a unit charged for the outdoor section alone is entered as 0, which makes the adjustment the whole line set rather than the difference, and in that case the indoor coil's own charge has to be added from the equipment's documentation as well.
Your ounces per foot is lower than the manufacturer's table. Which is right?
Theirs, and the difference is not an error in either. This page multiplies the tube's internal volume by the saturated liquid density at 77 °F, which is the honest computation. A manufacturer's published figure is usually a little larger because it is computed at a colder and therefore denser liquid and rounded in the safe direction, and because the warranty is written against their table rather than against anybody's arithmetic. Where the two disagree, weigh in to theirs and use this to check that the number is the right size.
Can I skip the scale and just charge on gauges?
Not on a system you have evacuated, no. A weighed charge starts from a known quantity; gauge readings on a system holding an unknown amount are a search rather than a measurement, and on a fixed orifice they depend on the weather at the moment you take them. The manifold's job comes afterwards: confirming that a weighed charge landed where the equipment expects, which is a different question from finding one by trial. A cylinder, a scale and this arithmetic get there in a single pass.
Does a long vertical lift change the charge?
Not the charge, but it changes whether the line set is acceptable at all, which is the bigger question. The refrigerant in the tube weighs what it weighs whether the tube is horizontal or standing on end, so the adjustment is a function of length and bore only. Lift matters to line sizing: an oversized suction riser stops carrying oil back to the compressor even while it flows perfectly well, and a large lift changes the pressure drop the metering device sees. Both come from the equipment's own line-sizing tables against the capacity and the equivalent length, and no charge calculation substitutes for them.
About line-set charge, and why weighing wins
The arithmetic here is short enough to state in a sentence: the internal volume of the liquid line, times the density of the liquid in it, times the number of feet by which the run differs from what the factory charged for. Everything interesting is in what is left out. The suction line is out because it carries vapor. The indoor coil is out because its charge is either in the nameplate figure or stated separately in the equipment's documentation. And the outside diameter is out of the calculation entirely — refrigeration tube is sold by its outside diameter, but what holds refrigerant is the bore, so the figure the page actually uses is the outside diameter less twice the wall, computed rather than looked up. That is also why the reference table below carries the suction sizes: they are there to show the magnitude of what is being excluded, not to be added in.
The method this supports is the one that starts from a known quantity. Evacuate the system, put the cylinder on a scale, and charge in the nameplate weight plus this adjustment. Everything else — topping up until the suction line feels right, charging until a sight glass clears, adding a bit because it is a hot day — starts from an unknown and hopes to converge, and on a fixed-orifice system it does so against a target that moves with the weather. Once the machine has run and settled, the gauges have a real job: verify on the side that means something for the metering device fitted, which is the subcooling calculator on a valve system and the superheat calculator on a piston. Those two pages check this one; they do not replace it.
Two failures are worth naming because they are common and they look nothing alike. The first is quiet: accepting a default line-set allowance without reading the plate. Fifteen feet is the commonest figure and it is not a rule, and if the unit was charged for twenty-five the answer is out by ten feet of liquid line in the wrong direction — on 3/8 in tube that is over five ounces, and it will show up later as a subcooling reading nobody can explain. The second is louder: treating the charge as the adjustment for a system that was the wrong size in the first place. Refrigerant does not fix capacity, and if the machine cannot keep up on a design day the question is how much load the building actually has, which is where the BTU calculator starts. This page sizes the charge for the equipment that is there; whether that equipment is right for the house is a separate calculation and a separate argument.
Where the line-set figures stay
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — loads, lengths, nameplate ratings, the rates your utility charges you — is uploaded, logged or kept, which is also why the calculators carry on working in a mechanical room with no signal.
The nameplate charge field starts empty on every visit rather than remembering the last unit you worked on, so one job's numbers cannot follow you into the next one.