Knowing the volume of a pipe run helps when filling a heating system with antifreeze, flushing or disinfecting a water main, calculating dead legs or estimating the weight of a full line on its supports. Use the inside diameter, not the nominal size.
How to use the Pipe Volume Calculator
- Inner diameter
- Pipe length
- Number of pipes
- Liquid
- Every result field is editable: type into Volume and Pipe length plus every other field update to match.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the inner diameter, the length of the run and the number of identical pipes, and pick the liquid.
Tips for an accurate estimate
- Measure inside dimensions of tanks and pools – wall thickness can change the volume noticeably.
- Use the average depth for pools with a sloping floor.
- Remember the weight: water weighs about 8.34 lb per US gallon (1 kg per litre), so large volumes need solid support.
- Check whether a figure is in US gallons, imperial gallons or litres before ordering chemicals or equipment.
Common mistakes to avoid
- Using wall height instead of water depth for above-ground pools.
- Assuming a horizontal tank’s volume is proportional to the liquid level – it is not.
- Mixing up flow units such as GPM, GPH and litres per minute.
Inputs explained
| Field | What to enter |
|---|---|
| Inner diameter | Units: in, mm, cm, m |
| Pipe length | Units: ft, m, in, yd, cm |
| Number of pipes | A number |
| Liquid | Choose one: Water, Seawater, Glycol 50%, Diesel … |
What each result means
- Volume = pi×([Inner diameter]÷2)^2×[Pipe length]×[Number of pipes]
- Weight of liquid = [Volume]×[Liquid]
- Volume per length = pi×([Inner diameter]÷2)^2
Example values
How the main result changes when Pipe length changes and everything else stays at the example values above:
| Pipe length (ft) | Volume (US gal) |
|---|---|
| 50 | 2.04 |
| 75 | 3.06 |
| 100 | 4.08 |
| 125 | 5.1 |
| 150 | 6.12 |
| 200 | 8.16 |
Formula
Volume = π × (ID ÷ 2)² × length × number of pipesMass = volume × liquid densityWorked example
Inputs — Inner diameter: 1 in; Pipe length: 100 ft; Number of pipes: 1; Liquid: Water.
Results — Volume = 4.08 US gal; Weight of liquid = 34.05 lb; Volume per length = 0.0408 gal/ft.
Frequently asked questions
How much water is in 100 ft of 1 in pipe?
About 4.1 gallons (15.4 L).
How do I calculate pipe volume?
π × (inner radius)² × length; for gallons with dimensions in inches and feet: 0.0408 × ID² × length.
Why use the inside diameter?
Nominal pipe sizes do not equal the bore; Schedule 40, 80 and copper types all have different inside diameters.
What formula does the Pipe Volume Calculator use?
Volume = π × (ID ÷ 2)² × length × number of pipes.