Pipe Volume Calculator

The pipe volume formula is V = π × (ID ÷ 2)² × length. Here is how to calculate pipe volume for any size: always use the inside diameter (ID), never the outside diameter, with ID and length in the same units. For example, 100 ft of 2-inch Sch 40 pipe (ID 2.067 in) holds 17.43 US gallons (65.99 litres, 2.33 ft³). Enter any ID and length in the pipe internal volume calculator above and it converts the result to gallons, litres, cubic feet and cubic metres automatically.

Multiply the bore area by 12 inches and divide by 231, since one US gallon is exactly 231 in³. A 2-inch Sch 40 pipe (ID 2.067 in) holds 0.1743 gallons per foot of pipe; a 4-inch Sch 40 pipe (ID 4.026 in) holds 0.6613 gallons per foot (8.2131 litres per metre). That is the pipe volume per foot for the most common sizes. The pipe volume chart below lists pipe volume in gallons per foot and litres per metre for every NPS size — click any row to load its ID into the calculator.

Inside diameter = outside diameter − 2 × wall thickness (ASME B36.10M). For example, NPS 4 Sch 40 has OD 4.500 in and a 0.237 in wall, so ID = 4.500 − 2 × 0.237 = 4.026 in. Watch out above NPS 8: Schedule 80 is not Extra Strong there — NPS 10 Sch 80 has a 0.594 in wall (ID 9.562 in). All 13 sizes are listed in the nps pipe inside diameter table below, which doubles as a standard pipe volume table with gallons per foot.

A partially filled horizontal pipe holds a circular segment: area = r² × arccos((r − d) ÷ r) − (r − d) × √(2rd − d²), where r is the inside radius and d is the fill depth — then multiply by length. This is the same circular segment area calculator pipe designers use for tank strapping tables. For example, a 12-inch-ID pipe, 50 ft long, filled 3 in deep holds 57.43 gallons — 19.55% of full. Use the Partial fill tab above: this partially filled pipe volume calculator accepts depth in inches or as a percentage of ID, and the built-in pipe fill calculator shows the fill percentage too.

Inside diameter. Capacity is the volume of the bore, so wall thickness does not count — if you only know the outside diameter, subtract twice the wall thickness (see the NPS table). Need the weight of the pipe metal itself instead of its capacity? That is a different job: use the Metal Weight Calculator, which works from OD × wall thickness and material density.

It depends on the true inside diameter, which follows different standards than steel NPS pipe — copper tube and PVC (for example Sch 40 PVC) have their own outside diameters and wall thicknesses, so look up or measure the actual ID and enter it above. A pvc pipe volume calculator uses exactly the same math; only the ID standard changes. Likewise, a copper pipe volume calculator just needs the CTS-based ID. As a rough scale reference, 1 in ID holds about 0.0408 gallons per foot and 2 in ID about 0.1632 gallons per foot.

Litres per metre = π × (ID in metres ÷ 2)² × 1000. A 4-inch Sch 40 pipe (ID 4.026 in = 102.26 mm) holds 8.2131 litres per metre — about 821.31 litres in a 100-metre run. Pipe volume litres per metre for every NPS size are in the table below, and the pipe capacity calculator at the top shows litres, gallons, ft³ and m³ for every result.

Divide the target volume by the bore area: length = volume ÷ (π × (ID ÷ 2)²). To hold 100 US gallons in 4-inch Sch 40 pipe (ID 4.026 in) you need 151.21 ft of pipe. Use the Volume → length tab above — it works as a length of pipe for volume calculator with targets in gallons, litres or ft³.

Pipe volume is static capacity — how much the pipe holds, in gallons. Flow rate is volume per unit time — how fast water moves, in gallons per minute (see the Gallons per Minute calculator). Velocity is the speed through the cross-section in ft/s (see the Pipe Velocity calculator), and Pipe Flow covers head loss and friction. This tool is the static side only; it never asks for time or pressure.

Work out each section's ID × length volume separately and add them up — the System volume tab is a pipe system volume calculator that does exactly that for up to 8 sections, with mixed inch/mm diameters and ft/m/in lengths. Fittings and valves add a little extra; for high accuracy, add their equivalent straight-pipe lengths.

Multiply gallons by 8.34 lb (the weight of one US gallon of water): 100 gallons weighs 834 lb. The volume of water in pipe calculator above shows water weight under every result. Note this is the weight of the contents — for the weight of the pipe metal itself, use the Metal Weight Calculator.