Stage count from the pressure ratio
Enter the inlet pressure and the target downstream pressure as gauge readings in psig. The page adds one standard atmosphere, taken as 14.696 psi (101.325 kPa), to convert them to absolute pressure in psia and works out the overall pressure ratio. It then compares that against the per stage ratio limit you entered, rounds the stage count up and splits the interstage settings geometrically so every stage carries the same ratio.
The standard atmosphere used for the conversion is a defined unit value. The per stage ratio limit, by contrast, depends on the valve type and the manufacturer and has not been confirmed in an authoritative source, so no reference figure is offered and you enter your own. Figures are current as of October 2026; check the valve data sheet as well.
Flow rate, flow coefficient, cavitation screening and valve sizing are not covered. Results show psia or psig first with kPa in parentheses; for example 150 psig down to 15 psig is a 5.546 : 1 absolute ratio. This calculator is for reference and does not replace design work; review by a qualified engineer is required.
Frequently Asked Questions
A pressure ratio only means something when it is measured from a true zero. Dividing one gauge pressure by another gives a ratio that is off by one atmosphere.
Giving every stage the same ratio keeps the load off any single valve. Real settings still have to be adjusted to the equipment on site.
No authoritative figure is offered. Enter the limit printed in the data sheet for the valve you are using.