Key Instruments: Flowmeter Manufacturing Technical Support

All standard flowmeters are calibrated at Standard Temperature and Pressure ("STP" 68°F/ 20°C and 14.7 psia/ 1 ATM).
When sizing a flowmeter that will operate at conditions other than "STP", it is important that the maximum flowrates of
the fluid be converted to equivalent standard flowrates of air or water. To do this, calculate the equivalent flowrates of
air or water at "STP" as shown below, then select the appropriate flowmeter for your application.

The correction factors that are calculated from the equations below should only be used for sizing

For Gases:

For Liquids:

Where:

Q_air

= Equivalent air flow at STP

Q_gas

= Maximum flow of gas

= Specific gravity of gas

T_act

= Absolute Temperature at flow
conditions in deg. K or deg. R

T_o

= Absolute temperature at STP,
in deg. K (294) or deg. R (530)

P_o

= Pressure at flow conditions (psia)

P_act

= Pressure at STP (14.7 psia)

Conversion Factors

To go from	Multiply by	To get
BAR	14.5	PSI
ATM	14.7	PSI
CCM	0.001	LPM
CCM	0.016	GPH
Gallon	3.785	Liters
GPH	62.5	CCM
GPM	3.785	LPM
GPM	.227	m³/hr
LPM	1000	CCM
LPM	0.2642	GPM
LPM	2.119	ft³/hr
LPM	0.0353	ft³/min
SCFM	28.31	LPM
SCFH	472	CCM
SCFH	0.472	LPM