1 1/2 in schedule 40 pipe flow and volume calculator
1 1/2 in schedule 40 pipe has an outside diameter of 48.3 mm and a bore of 40.9 mm, a wall thickness of 3.70 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
- 31.237
- Inside diameter
- 40.90
- Wall thickness
- 3.700
- Bore area
- 1313.82 mm2
- Water content per metre
- 1.3138
- Water in the run
- 32.85
- Weight of that water
- 32.85
- Friction head loss
- 1.592
- Pressure drop
- 15.615 kPa
Show the working
- Flow velocity = 1.5
- Pipe run = 25
- Hazen-Williams C = 140
- Fluid density = 1000
- Inside diameter = 40.9 = 40.9
- outside = 48.3 = 48.3
- Wall thickness = (48.3 - 40.9) / 2 = 3.7
- Bore area = pi * 40.9^2 / 4 = 1313.82
- area_m2 = 1313.82 / 1e6 = 0.001 313 82
- Water content per metre = 1313.82 / 1000 = 1.313 82
- Water in the run = 1.313 82 * 25 = 32.8455
- flow_m3s = 0.001 313 82 * 1.5 = 0.001 970 73
- Flow at that velocity = 0.001 970 73 * 60000 = 118.244
- Flow in US gallons per minute = 118.244 / 3.785411784 = 31.2368
- loss_per_m = 10.67 * (0.001 970 73)^1.852 / (140^1.852 * (40.9/1000)^4.87) = 0.063 693 2
- Friction head loss = 0.063 693 2 * 25 = 1.592 33
- Pressure drop = 1.592 33 * 1000 * g0 / 1000 = 15.6154
- Weight of that water = 32.8455 * 1000 / 1000 = 32.8455
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.
1 1/2 in pipe at common velocities
| Velocity (m/s) | Flow (L/min) | Flow (US gpm) |
|---|---|---|
| 0.5 | 39.4 | 10.41 |
| 1 | 78.8 | 20.82 |
| 1.5 | 118.2 | 31.24 |
| 2 | 157.7 | 41.65 |
| 2.5 | 197.1 | 52.06 |
| 3 | 236.5 | 62.47 |
Frequently asked
What is the inside diameter of 1 1/2 in schedule 40 pipe?
40.9 mm, against an outside diameter of 48.3 mm.
How much water does 1 1/2 in pipe hold?
1.314 litres per metre of run.
Where the numbers come from
- Dimensions are the ASME B36.10 schedule 40 values for the nominal size.