20 in schedule 40 pipe flow and volume calculator
20 in schedule 40 pipe has an outside diameter of 508 mm and a bore of 477.8 mm, a wall thickness of 15.10 mm. Nominal pipe size is a label, not a measurement — nothing about a 1-inch pipe is one inch.
Domestic water is usually kept between 1 and 2.4 m/s to limit noise and erosion.
Copper and plastic about 140; new steel 130; old steel 100.
- Flow in US gallons per minute
- 4262.963
- Inside diameter
- 477.80
- Wall thickness
- 15.100
- Bore area
- 179 300.78 mm2
- Water content per metre
- 179.3008
- Water in the run
- 4482.52
- Weight of that water
- 4482.52
- Friction head loss
- 0.091
- Pressure drop
- 0.889 kPa
Show the working
- Flow velocity = 1.5
- Pipe run = 25
- Hazen-Williams C = 140
- Fluid density = 1000
- Inside diameter = 477.8 = 477.8
- outside = 508 = 508
- Wall thickness = (508 - 477.8) / 2 = 15.1
- Bore area = pi * 477.8^2 / 4 = 179 301
- area_m2 = 179 301 / 1e6 = 0.179 301
- Water content per metre = 179 301 / 1000 = 179.301
- Water in the run = 179.301 * 25 = 4482.52
- flow_m3s = 0.179 301 * 1.5 = 0.268 951
- Flow at that velocity = 0.268 951 * 60000 = 16 137.1
- Flow in US gallons per minute = 16 137.1 / 3.785411784 = 4262.96
- loss_per_m = 10.67 * (0.268 951)^1.852 / (140^1.852 * (477.8/1000)^4.87) = 0.003 625 45
- Friction head loss = 0.003 625 45 * 25 = 0.090 636 2
- Pressure drop = 0.090 636 2 * 1000 * g0 / 1000 = 0.888 838
- Weight of that water = 4482.52 * 1000 / 1000 = 4482.52
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
Scenarios & local history
Compare a saved scenario
Recent calculations
The formula
- bore area = pi d^2 / 4
- flow = area x velocity
- Hazen-Williams head loss per metre = 10.67 Q^1.852 / (C^1.852 d^4.87), SI units
Nominal pipe size is a legacy label. Above 14 inch NPS the outside diameter equals the nominal size; below it, neither dimension matches.
Hazen-Williams is an empirical formula fitted to water near room temperature. For other fluids or for gases, use Darcy-Weisbach.
Fittings add loss too. A rule of thumb is to add 30 to 50% to the straight-run figure for a typical domestic circuit.
20 in pipe at common velocities
| Velocity (m/s) | Flow (L/min) | Flow (US gpm) |
|---|---|---|
| 0.5 | 5379.0 | 1420.99 |
| 1 | 10758.0 | 2841.98 |
| 1.5 | 16137.1 | 4262.96 |
| 2 | 21516.1 | 5683.95 |
| 2.5 | 26895.1 | 7104.94 |
| 3 | 32274.1 | 8525.93 |
Frequently asked
What is the inside diameter of 20 in schedule 40 pipe?
477.8 mm, against an outside diameter of 508 mm.
How much water does 20 in pipe hold?
179.301 litres per metre of run.
Where the numbers come from
- Dimensions are the ASME B36.10 schedule 40 values for the nominal size.