AC Refrigerant Recharge Calculator
Estimate how much refrigerant to add to a partially charged car air-conditioning system and how many cans it takes to top it back up.
How it works
To add = full charge × (1 − current%) · Cans = ceil(to add ÷ can size)
A car AC system holds a precise refrigerant charge printed on an underhood label. The amount to add is the shortfall from full — the full charge times the fraction currently missing — and dividing by the can size, rounded up, gives the cans to buy. Because overcharging harms cooling and can damage the compressor, the only accurate way to fill is by weight after evacuating; topping up by cans is a rough field estimate, best done watching low-side pressure on a gauge.
Worked example
A system that holds 28 oz reading roughly 60% charged already contains 16.8 oz, so it needs 28 − 16.8 = 11.2 oz. From 12 oz cans that is one can, added slowly while watching the low-side gauge.
Frequently asked questions
How much refrigerant does a car AC hold?
Most cars take about 18–36 ounces (roughly 500–1,000 g). The exact figure is on a label under the hood or in the service manual — always use that number rather than a guess.
Can I overcharge the system with a can?
Yes, and it is a real risk. Too much refrigerant raises pressures, cuts cooling and can damage the compressor. Add slowly, watch the low-side pressure, and stop when it reaches spec rather than emptying the whole can blindly.
Why is charging by weight more accurate?
Pressure varies with temperature and humidity, so gauge readings only approximate the charge. A shop evacuates the system and refills the exact labelled weight, which is why professional recharges cool better and last longer.
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This calculator is for educational purposes. Double-check important results before acting on them.