Pipe Volume Calculator
Estimate water or material volume inside a circular pipe from inside diameter and length, including gallons, gallons per foot, and cubic feet. Use it for pipeline fill, disinfection volume, hydrostatic test water, or comparing pipe displacement.
Enter your values, then press Calculate.
How to calculate
Enter the inside diameter (not OD unless the wall is negligible) and the pipe length. Diameter is usually inches on the spec sheet; length is usually feet. To read gallons per foot, enter length as 1 ft, or divide the gallon result by the length in feet.
Formula
Radius (ft) = ID / 2. Volume (ft³) = π × r² × length. Gallons = ft³ × 7.48051948. Cubic yards = ft³ ÷ 27. Gallons per foot = gallons ÷ length (ft).
Common use cases
- Chlorination / disinfection volume
- Hydrostatic test water
- Pipeline fill volume
- Gallons per foot of pipe
- Pipe displacement vs backfill
- Comparing 6 in, 8 in, and 12 in ID
Assumptions
- Diameter is inside diameter (ID), not outside diameter and not nominal pipe size if the wall is thick.
- The section is a full circular prism. Partial flow is not modeled.
- Gallons = cubic feet × 7.48052. Gallons per foot = total gallons ÷ length in feet.
- Length is centerline length of the run you are filling.
Limitations
- Does not compute flow, velocity, or Manning n.
- Does not use wall thickness or OD. For trench displacement, use the backfill pipe deduction with OD.
- Does not add fittings, valves, or services.
- Does not apply a disinfection contact-time standard; it only gives volume.
Worked examples
12 in ID × 100 ft
Full 12 in inside diameter for 100 ft. Interior volume is 78.54 ft³ = 587.5 gallons, or 5.875 gal/ft.
1. Cross-section area
π × (1 / 2)² = 0.7854 ft²
2. Volume
0.7854 × 100 = 78.5398 ft³
3. Gallons
78.5398 × 7.48051948 = 587.5186 gal
4. Gallons per foot
587.5186 ÷ 100 = 5.8752 gal/ft
6 in ID × 1 ft (gallons per foot)
Length 1 ft isolates gallons per foot: 1.4688 gal/ft at 6 in ID, full pipe.
1. Cross-section area
π × (0.5 / 2)² = 0.1963 ft²
2. Volume
0.1963 × 1 = 0.1963 ft³
3. Gallons
0.1963 × 7.48051948 = 1.4688 gal
4. Gallons per foot
1.4688 ÷ 1 = 1.4688 gal/ft
Gallons per foot of pipe
Gallons per foot equals total gallons divided by length. Enter inside diameter and a 1 ft length to read gallons per foot directly. Example using the live calculator: 6 in ID × 1 ft = 1.47 gal, which is 1.4688 gal/ft. This is the same full circular prism as the main result; it does not assume a nominal pipe size or wall thickness.
Pipeline fill volume
Pipeline fill volume is the full interior volume of the run. Use this page for disinfection volume, hydrostatic test water, and fill estimates. Partial flow and slope are not applied; use the pipe slope calculator when you need grade on the same run.
Interior fill versus trench displacement
Fill, pressure test, and chlorination care about water inside the pipe — ID. Spoil displacement and backfill deduction care about the hole the pipe occupies — OD. A 12 in ID × 100 ft line holds 587.5 gallons (5.875 gal/ft). The same stick of ductile iron may have a larger OD; that larger circle belongs on the backfill page, not here.
Related calculators
- Pipe Slope CalculatorConvert elevation drop and run into percent grade, ratio, and inches per foot.
- Bedding CalculatorEstimate pipe bedding cubic yards from length, width, and depth.
- Backfill CalculatorEstimate trench backfill cubic yards after subtracting pipe displacement.
- Percent Grade CalculatorConvert rise and run into percent grade, slope ratio, and feet per 100 feet.
- Trench Excavation CalculatorConvert trench length, width, and depth into cubic yards of excavation.
- Trench Spoils CalculatorConvert bank trench yards to loose spoils and truckloads using a swell factor.
- Truckload EstimatorConvert cubic yards into truckloads using a real truck capacity.
FAQ
ID or OD?
Liquid volume uses inside diameter. For trench displacement / backfill deduction, the backfill calculator wants outside diameter.
Is the pipe assumed full?
Yes. The result is the full circular prism. Partial flow or slope is not applied.
How do I calculate gallons per foot of pipe?
Divide total gallons by length in feet, or enter length as 1 ft. For 6 in inside diameter the live formula gives 1.4688 gal/ft. Wall thickness is not used; this is interior volume from ID.
Can I use this as a pipeline fill calculator?
Yes for a full circular line. The result is the interior prism from inside diameter and length. It does not apply partial flow, fittings, or slope. Use pipe slope when you need grade on the same run.
How many gallons are in a 6 inch pipe per foot?
1.4688 gallons per foot at 6 in inside diameter (full pipe, ID not OD). An 8 in ID pipe is 2.6112 gal/ft.
Does this work for tubing capacity?
Yes if you enter the tubing inside diameter and length. The model is a circular prism, so it fits pipe or tubing when ID is known. Do not enter OD unless the wall is negligible.
Nominal 12 in PVC — ID or 12.00 in?
Use the published inside diameter from the manufacturer, which is often slightly less than 12 in for IPS. Typing 12 in is an estimate, not a catalog ID.
Disclaimer
These calculators are estimating tools for planning and field checks. They are not a substitute for approved plans, specifications, licensed professional engineering, or governing standards. Confirm densities, waste factors, and yields with your supplier and project documents.