8 in schedule 40 pipe flow and volume calculator
8 in schedule 40 pipe has an outside diameter of 219.1 mm and a bore of 202.7 mm, a wall thickness of 8.20 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
- 767.232
- Inside diameter
- 202.70
- Wall thickness
- 8.200
- Bore area
- 32 269.88 mm2
- Water content per metre
- 32.2699
- Water in the run
- 806.75
- Weight of that water
- 806.75
- Friction head loss
- 0.246
- Pressure drop
- 2.416 kPa
Show the working
- Flow velocity = 1.5
- Pipe run = 25
- Hazen-Williams C = 140
- Fluid density = 1000
- Inside diameter = 202.7 = 202.7
- outside = 219.1 = 219.1
- Wall thickness = (219.1 - 202.7) / 2 = 8.2
- Bore area = pi * 202.7^2 / 4 = 32 269.9
- area_m2 = 32 269.9 / 1e6 = 0.032 269 9
- Water content per metre = 32 269.9 / 1000 = 32.2699
- Water in the run = 32.2699 * 25 = 806.747
- flow_m3s = 0.032 269 9 * 1.5 = 0.048 404 8
- Flow at that velocity = 0.048 404 8 * 60000 = 2904.29
- Flow in US gallons per minute = 2904.29 / 3.785411784 = 767.232
- loss_per_m = 10.67 * (0.048 404 8)^1.852 / (140^1.852 * (202.7/1000)^4.87) = 0.009 853 06
- Friction head loss = 0.009 853 06 * 25 = 0.246 327
- Pressure drop = 0.246 327 * 1000 * g0 / 1000 = 2.415 64
- Weight of that water = 806.747 * 1000 / 1000 = 806.747
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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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.
8 in pipe at common velocities
| Velocity (m/s) | Flow (L/min) | Flow (US gpm) |
|---|---|---|
| 0.5 | 968.1 | 255.74 |
| 1 | 1936.2 | 511.49 |
| 1.5 | 2904.3 | 767.23 |
| 2 | 3872.4 | 1022.98 |
| 2.5 | 4840.5 | 1278.72 |
| 3 | 5808.6 | 1534.46 |
Frequently asked
What is the inside diameter of 8 in schedule 40 pipe?
202.7 mm, against an outside diameter of 219.1 mm.
How much water does 8 in pipe hold?
32.270 litres per metre of run.
Where the numbers come from
- Dimensions are the ASME B36.10 schedule 40 values for the nominal size.