Pressure, flow and temperature conversions for valve and pipework specification, plus the nominal bore designations in millimetres and inches.
Pressure
| bar | — |
|---|---|
| kg/cm² (at) | — |
| psi (lbf/in²) | — |
| kPa | — |
| MPa | — |
| metres water col. | — |
| atm | — |
kg/cm² is not the same as bar: 1 kg/cm² is 0.9807 bar. Test certificates quote kg/cm², valve bodies are rated in bar or PN, and treating them as equal is a 2% error.
Flow
| m³/h | — |
|---|---|
| litres/min | — |
| litres/sec | — |
| US gallons/min | — |
| Imp. gallons/min | — |
| ft³/min | — |
Temperature
Type in either box. A valve’s pressure rating falls as temperature rises — the class on the body is its cold rating.
Nominal bore
Nominal sizes are designations, not measurements: 50 mm bore is 2 inches, not 1.97. Convert by looking up, never by multiplying.
| mm | Inches | mm | Inches |
|---|---|---|---|
| 8 | 1/4" | 125 | 5" |
| 10 | 3/8" | 150 | 6" |
| 15 | 1/2" | 200 | 8" |
| 20 | 3/4" | 250 | 10" |
| 25 | 1" | 300 | 12" |
| 32 | 1 1/4" | 350 | 14" |
| 40 | 1 1/2" | 400 | 16" |
| 50 | 2" | 450 | 18" |
| 65 | 2 1/2" | 500 | 20" |
| 80 | 3" | 600 | 24" |
| 100 | 4" |
Pressure classes at a glance
| bar | kg/cm² | psi | kPa | MPa |
|---|---|---|---|---|
| 1 | 1.02 | 14.5 | 100 | 0.10 |
| 1.6 | 1.63 | 23.2 | 160 | 0.16 |
| 2.5 | 2.55 | 36.3 | 250 | 0.25 |
| 4 | 4.08 | 58.0 | 400 | 0.40 |
| 6 | 6.12 | 87.0 | 600 | 0.60 |
| 10 | 10.20 | 145.0 | 1,000 | 1.00 |
| 16 | 16.32 | 232.1 | 1,600 | 1.60 |
| 25 | 25.49 | 362.6 | 2,500 | 2.50 |
| 40 | 40.79 | 580.2 | 4,000 | 4.00 |
| 64 | 65.26 | 928.2 | 6,400 | 6.40 |
| 100 | 101.97 | 1,450.4 | 10,000 | 10.00 |
PN 16 means the body is rated 16 bar cold. Sant states the same rating as PN 1.6 in MPa on some pages — the two are one class, not two.
Common questions
Is kg/cm² the same as bar?
No — 1 kg/cm² equals 0.980665 bar, not 1:1. Test certificates are usually quoted in kg/cm² while a body rating is usually quoted in bar; treating them as interchangeable is a 2% error that matters on a certificate.
Why is nominal bore a lookup table instead of a millimetre-to-inch conversion?
Because a nominal size is a designation, not a measurement — 50 mm nominal bore is called 2", not 1.97". Converting it by simple arithmetic is one of the commonest ways to order the wrong pipe schedule.
Is PN 16 the same rating as PN 1.6?
Yes — PN 16 (bar) and PN 1.6 (MPa) are the same pressure class written two ways. Some brands print one notation, some the other, on different pages of the same price list.