Enter the installed line length, the manufacturer's pre-charged length, and the liquid line size to estimate the additional refrigerant charge needed.
Most split-system air conditioners and heat pumps ship pre-charged with refrigerant for a standard line-set length — commonly 15 feet. Run longer lines than that during installation, and the system needs extra refrigerant added to make up the difference, or it runs low and underperforms.
How to Use the Refrigerant Line Charge Calculator
Enter the total installed line length and the length already covered by the factory pre-charge, then pick the liquid line's diameter from the dropdown to set its charge rate in ounces per foot.
additional charge (oz) = (total length − pre-charged length) × oz per footA 1/2" liquid line carries roughly four times the refrigerant per foot that a 1/4" line does, simply because it holds more volume — line diameter matters here as much as length does. This calculator zeroes out the result automatically if the installed run is shorter than the pre-charged length, since no addition is needed in that case.
Nothing here replaces the manufacturer's charging chart for a specific unit. Real-world charging also accounts for elevation change between the indoor and outdoor units and a subcooling or superheat check at startup, neither of which this estimate sees — use it to get a rough ounce figure ahead of the job, then verify against gauges and the unit's actual spec sheet before sealing anything up.