The calculator on this page will convert gallons per minute (GPM) into the following volume/flow quantities:
- CFS – cubic feet per second
- CFM – cubic feet per minute
- AFA – acre feet per annum
- MI – miners inches (see the discussion following the calculator, the values differ from state to state)
Values used in the calculator.
- 1 gpm = 0.1114 MI (where 50 MI=1 CFS)*
- 1 gpm = 0.0891 MI (where 40 MI=1 CFS)*
- 1 gpm = 0.0855 MI (where 38.4 MI=1 CFS)*
- 1 gpm = 0.1337 CFM
- 1 gpm = 0.002228 CFS
- 1 gpm = 1.612 AFA
* Different states use different values for miner’s inches. See the discussion following the calculator.
How to use the calculator.
- Enter the number of gallons per minute you wish to convert in the top of the form. DO NOT USE COMMAS.
- Select MI, CFM, CFS or AFA.
- Click “Calculate. The converted expression will appear in the last box (conversion). If you selected CFS, the converted figure is an expression in CFS. To recalculate with a different expression (for example, AFA instead of CFS), be sure to select AFA, and click the calculate button again so that the math will reset.
To test the calculator, use 1 GPM. The results will match the formula above.
Notes about miner’s inches.
A miner’s inch is not a measure of length, but it is the measurement of the rate of water flow in a miner’s sluice. Flow was measured by a hole one inch square with a head of one inch. Generally, one miner’s inch is a flow of 1.5 cubic feet per minute You will find references to “miner’s inches” in old water right filings and notices, as well as older decrees governing water rights.
As water demand increased with the development of large-scale mining technologies and the development of irrigation uses, the miner’s inch became an inadequate unit of measurement for flow rates, and was replaced by cubic feet per second.
A miner’s inch is not the same in all of the states:
| State | Number of miner's inches per CFS (cubic foot per second) |
| Idaho, Kansas, Nebraska, New Mexico, North Dakota, South Dakota | ......50 miner's inches |
| Arizona, California, Montana, Oregon | ......40 miner's inches |
| Other states | ......38.4 miner's inches |
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