US gallons per minute to cubic feet per minute

HVAC engineers routinely compare a cooling tower's water flow in gallons per minute with its air flow in cubic feet per minute — two fluids, two flow units, one chiller. The bridge is 0.1336805556, the exact CFM in one GPM: the 231 in³ gallon divided by the 1,728 in³ cubic foot. A 60 GPM condenser water loop is 8.02 CFM of water, against which the tower might move 10,000 CFM of air.

1 US gallon per minute = 0.13368056 cubic feet per minute, and 1 cubic foot per minute = 7.48052 US gallons per minute. One fixed factor covers the whole range: multiply US gal/min by 0.13368056. Worked: 10 US gal/min = 1.3368056 CFM; 100 US gal/min = 13.368056 CFM.

By EnginStack Editorial Team | Reviewed against NIST, BIPM and primary-source documentation About →
US gallons per minute
8.02083333 cubic feet per minute
60 US gallons per minute = 8.02083333 cubic feet per minute 60 cubic feet per minute = 448.83116883 US gallons per minute

Verified against NIST Special Publication 811 and BIPM SI definitions. The conversion factor is exact and traceable to the 1959 treaty constants.

US gallons per minute to cubic feet per minute

The factor is exact because both units are inch-derived volumes: one gallon is 231 in³ and one cubic foot is 1,728 in³, so one GPM is 231/1,728 = 0.1336805556 CFM. This is the only non-decimal factor in the flow family on this site — the rest chain through the liter — and it is the one HVAC technicians hit when balancing water-side and air-side flows. The reciprocal is 7.4805194805, the famous gallons-in-a-cubic-foot number that appears in every tank and pool calculation.

cubic feet per minute = US gallons per minute × 0.1336805556
1 GPM = 0.1336805556 CFM — 231 in³ ÷ 1,728 in³
The factor is exact from both inch-volume definitions.

Worked Examples

Example 1: Find the air side of a 20 GPM condenser loop

20 × 0.1336805556 = 2.67 CFM

Example 2: Convert a 300 GPM chiller flow

300 × 0.1336805556 = 40.10 CFM

Example 3: Scale a 2,000 GPM plant cooling circuit

2,000 × 0.1336805556 = 267.36 CFM

Common US gallons per minute to cubic feet per minute Conversions

US gallons per minutecubic feet per minuteContext
1 GPM0.1337 CFMThe definitional anchor.
60 GPM8.02 CFMA small condenser water loop.
100 GPM13.37 CFMA chiller's water flow.
500 GPM66.84 CFMA large cooling tower water flow.
1,000 GPM133.7 CFMA plant cooling circuit.

Engineering Context

This page carries the only inch-to-inch flow factor in the family — it is the gallons to cubic feet volume conversion applied per minute. The CFM to GPM page runs it backward, and the flow rate hub collects the full family. Chiller water loops also connect to the energy pages, since flow × temperature drop carries the cooling load.

This direction is the one that gets used in a heat balance, because equipment is specified by water flow far more often than by air flow. The common rule of thumb in chiller work is about 3 GPM per ton of refrigeration on the evaporator and roughly 4.5 GPM per ton on the condenser, which is why condenser water loops cluster in the 2 to 3 CFM per 100 GPM band when the air side is stated. Treat those ratios as design shortcuts, not as conversions: the exact factor here is still 231 ÷ 1,728 and carries no uncertainty, while the GPM-per-ton figure depends on the temperature difference you have chosen.

More: CFM to GPM · GPM to L/min · gal to ft³ · Flow Rate Guide · Flow Rate Hub

Related Unit Converters

cubic feet per minute to US gallons per minute US gallons per minute to liters per minute Gallons to Cubic Feet Flow Rate Conversion Guide Flow Rate Converters

Frequently Asked Questions

How many CFM is 1 GPM?

Exactly 0.1336805556. One US gallon is 231 in³ and one cubic foot is 1,728 in³, so the ratio is 231/1,728 — exact by definition.

Why compare water GPM with air CFM?

Because cooling towers and chillers balance two fluids: the water loop carries heat away from the building, and the air stream carries it to the atmosphere. Sizing both sides of that balance means converting between the two flow units.

Is 7.48 gallons per cubic foot the same factor?

Yes — 1 ft³ = 7.4805194805 US gallons is the exact reciprocal of the 0.13368 here. It is the same ratio seen from the other side, and it appears in every tank sizing and pool volume calculation.