# EPANET: Measurement Units

Measurement Units

The toolkit can use data expressed in either US Customary of SI Metric units. A project's unit system depends on the unit system used for its choice of flow units. If the EN_open function is used to supply data to a project from an Input File then its flow units are set in the [OPTIONS] section of the file. If the EN_init function is used to initialize a project then the choice of flow units is the fourth argument to the function. The following table lists the units used to express the various parameters in an EPANET model.

Parameter | US Customary | SI Metric
--- | --- | ---
Concentration | mg/L or ug/L | mg/L or ug/L
Demand | (see Flow units) | (see Flow units)
Diameter (Pipes) | inches | millimeters
Diameter (Tanks) | feet | meters
Efficiency | percent | percent
Elevation | feet | meters
Emitter Coeff. | flow units @ 1 psi drop | flow units @ 1 meter drop
Energy | kwatt - hours | kwatt - hours
Flow | CFS (cubic feet / sec) | LPS (liters / sec)
| GPM (gallons / min) | LPM (liters / min)
| MGD (million gal / day) | MLD (megaliters / day)
| IMGD (Imperial MGD) | CMH (cubic meters / hr)
| AFD (acre-feet / day) | CMD (cubic meters / day)
Friction Factor | unitless | unitless
Head | feet | meters
Length | feet | meters
Minor Loss Coeff. | unitless | unitless
Power | horsepower | kwatts
Pressure | psi | meters
Reaction Coeff. (Bulk) | 1/day (1st-order) | 1/day (1st-order)
Reaction Coeff. (Wall) | mass/sq-ft/day (0-order) | mass/sq-m/day (0-order)
| ft/day (1st-order) | meters/day (1st-order)
Roughness Coeff. | millifeet (Darcy-Weisbach) unitless otherwise | mm (Darcy-Weisbach) unitless otherwise
Source Mass Injection | mass/minute | mass/minute
Velocity | ft/sec | meters/sec
Volume | cubic feet | cubic meters
Water Age | hours | hours