3 1/2 in schedule 40 pipe flow and volume calculator
3 1/2 in schedule 40 pipe has an outside diameter of 101.6 mm and a bore of 90.1 mm, a wall thickness of 5.75 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
- 151.589
- Inside diameter
- 90.10
- Wall thickness
- 5.750
- Bore area
- 6375.87 mm2
- Water content per metre
- 6.3759
- Water in the run
- 159.40
- Weight of that water
- 159.40
- Friction head loss
- 0.634
- Pressure drop
- 6.217 kPa
Show the working
- Flow velocity = 1.5
- Pipe run = 25
- Hazen-Williams C = 140
- Fluid density = 1000
- Inside diameter = 90.1 = 90.1
- outside = 101.6 = 101.6
- Wall thickness = (101.6 - 90.1) / 2 = 5.75
- Bore area = pi * 90.1^2 / 4 = 6375.87
- area_m2 = 6375.87 / 1e6 = 0.006 375 87
- Water content per metre = 6375.87 / 1000 = 6.375 87
- Water in the run = 6.375 87 * 25 = 159.397
- flow_m3s = 0.006 375 87 * 1.5 = 0.009 563 81
- Flow at that velocity = 0.009 563 81 * 60000 = 573.828
- Flow in US gallons per minute = 573.828 / 3.785411784 = 151.589
- loss_per_m = 10.67 * (0.009 563 81)^1.852 / (140^1.852 * (90.1/1000)^4.87) = 0.025 360 3
- Friction head loss = 0.025 360 3 * 25 = 0.634 006
- Pressure drop = 0.634 006 * 1000 * g0 / 1000 = 6.217 48
- Weight of that water = 159.397 * 1000 / 1000 = 159.397
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.
3 1/2 in pipe at common velocities
| Velocity (m/s) | Flow (L/min) | Flow (US gpm) |
|---|---|---|
| 0.5 | 191.3 | 50.53 |
| 1 | 382.6 | 101.06 |
| 1.5 | 573.8 | 151.59 |
| 2 | 765.1 | 202.12 |
| 2.5 | 956.4 | 252.65 |
| 3 | 1147.7 | 303.18 |
Frequently asked
What is the inside diameter of 3 1/2 in schedule 40 pipe?
90.1 mm, against an outside diameter of 101.6 mm.
How much water does 3 1/2 in pipe hold?
6.376 litres per metre of run.
Where the numbers come from
- Dimensions are the ASME B36.10 schedule 40 values for the nominal size.