12 in schedule 40 pipe flow and volume calculator
12 in schedule 40 pipe has an outside diameter of 323.9 mm and a bore of 303.2 mm, a wall thickness of 10.35 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
- 1716.634
- Inside diameter
- 303.20
- Wall thickness
- 10.350
- Bore area
- 72 201.84 mm2
- Water content per metre
- 72.2018
- Water in the run
- 1805.05
- Weight of that water
- 1805.05
- Friction head loss
- 0.154
- Pressure drop
- 1.511 kPa
Show the working
- Flow velocity = 1.5
- Pipe run = 25
- Hazen-Williams C = 140
- Fluid density = 1000
- Inside diameter = 303.2 = 303.2
- outside = 323.9 = 323.9
- Wall thickness = (323.9 - 303.2) / 2 = 10.35
- Bore area = pi * 303.2^2 / 4 = 72 201.8
- area_m2 = 72 201.8 / 1e6 = 0.072 201 8
- Water content per metre = 72 201.8 / 1000 = 72.2018
- Water in the run = 72.2018 * 25 = 1805.05
- flow_m3s = 0.072 201 8 * 1.5 = 0.108 303
- Flow at that velocity = 0.108 303 * 60000 = 6498.17
- Flow in US gallons per minute = 6498.17 / 3.785411784 = 1716.63
- loss_per_m = 10.67 * (0.108 303)^1.852 / (140^1.852 * (303.2/1000)^4.87) = 0.006 161 22
- Friction head loss = 0.006 161 22 * 25 = 0.154 03
- Pressure drop = 0.154 03 * 1000 * g0 / 1000 = 1.510 52
- Weight of that water = 1805.05 * 1000 / 1000 = 1805.05
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.
12 in pipe at common velocities
| Velocity (m/s) | Flow (L/min) | Flow (US gpm) |
|---|---|---|
| 0.5 | 2166.1 | 572.21 |
| 1 | 4332.1 | 1144.42 |
| 1.5 | 6498.2 | 1716.63 |
| 2 | 8664.2 | 2288.85 |
| 2.5 | 10830.3 | 2861.06 |
| 3 | 12996.3 | 3433.27 |
Frequently asked
What is the inside diameter of 12 in schedule 40 pipe?
303.2 mm, against an outside diameter of 323.9 mm.
How much water does 12 in pipe hold?
72.202 litres per metre of run.
Where the numbers come from
- Dimensions are the ASME B36.10 schedule 40 values for the nominal size.