About Pipe Volume Calculator — Gallons & Liters in a Pipe Run
The pipe volume calculator computes how much liquid a straight run of pipe holds: enter the inside diameter — directly, or by picking a nominal Schedule 40 size whose true ID comes from the ASME B36.10M dimension table — plus the run length, and the tool returns the volume in cubic feet, US gallons, liters, and cubic metres, along with the weight of that much water. The classic trap this tool avoids is nominal-vs-actual: a "2-inch" Sch 40 steel pipe actually measures 2.067 in inside, and a "½-inch" only 0.622 in, so volumes computed from nominal sizes run wrong in both directions.
The conversions are pinned to exact definitions: a US gallon is exactly 231 in³, so one cubic foot is 1728/231 = 7.480519 gallons, and water at 60 °F weighs 62.37 lb/ft³ (CRC Handbook) — the number that turns a drained-down fire main or a filled hydronic loop into pounds the structure or the truck has to carry. Use it for chlorination dosing, glycol fill quantities, drain-down volumes, and weight checks on filled lines.
How It Works
- Pick a Schedule 40 nominal size (½″ through 6″) to load its verified inside diameter, or choose custom entry and type any ID up to 48 in / 1,219.2 mm — for copper, PEX, PVC, or other schedules, enter that pipe's actual ID.
- Enter the run length. The imperial/metric toggle converts your entries in place (rounded to field precision and clamped to the caps), so nothing errors out when you switch.
- Read the volume four ways — ft³, US gallons, liters, m³ — plus the contained-water weight in lb and kg at the 60 °F density.
- For per-foot figures, enter 100 ft and shift the decimal: the chart below tabulates gallons per 100 ft for the common Sch 40 sizes.
Worked Example
How much water sits in 100 ft of 2-inch Schedule 40 steel pipe? The true ID is 2.067 in (ASME B36.10M) = 0.17225 ft, so V = π × (0.17225/2)² × 100 = 2.330 ft³. In gallons: 2.330 × 7.480519 = 17.43 gal — call it a sixth of a gallon per foot. That water weighs 2.330 × 62.37 = 145.3 lb (65.9 kg), which is why a filled riser is a structural load and why drain-down volumes surprise people: the "small" 2-inch line across a 100 ft building holds two full buckets more than 17 gallons.
How much water is in a pipe? Gallons per 100 ft of Sch 40
Water volume and weight in 100 ft of Schedule 40 steel pipe, computed through the calculator from the ASME B36.10M inside diameters (not the nominal sizes) at 62.37 lb/ft³ (60 °F). For a different run length, scale linearly — 250 ft of 1″ holds 2.5 × the 1″ row.
| Nominal size (Sch 40) | Inside diameter (in) | Gallons per 100 ft | Water weight (lb) |
|---|---|---|---|
| ½″ | 0.622 | 1.58 | 13.16 |
| ¾″ | 0.824 | 2.77 | 23.10 |
| 1″ | 1.049 | 4.49 | 37.43 |
| 2″ | 2.067 | 17.43 | 145.34 |
| 4″ | 4.026 | 66.13 | 551.38 |
| 6″ | 6.065 | 150.08 | 1,251.31 |
Formulas
- Pipe volume
V = π × (ID/2)² × L- Gallons from cubic feet
gal = ft³ × 7.480519- Water weight
lb = ft³ × 62.37; kg = lb × 0.45359237- Sch 40 inside diameters (in), ASME B36.10M
½″ 0.622 · ¾″ 0.824 · 1″ 1.049 · 1¼″ 1.380 · 1½″ 1.610 · 2″ 2.067 · 3″ 3.068 · 4″ 4.026 · 6″ 6.065
Standards & References
- ASME B36.10M, Welded and Seamless Wrought Steel Pipe — Schedule 40 dimension table (inside diameters verified against published tables)
- US gallon = 231 in³ exactly (NIST Handbook 44, Appendix C); 1 ft³ = 7.480519 gal
- Water unit weight 62.37 lb/ft³ at 60 °F — CRC Handbook of Chemistry and Physics water-density tables
Frequently Asked Questions
How many gallons of water are in 100 feet of 2-inch pipe?
For 2″ Schedule 40 steel (true ID 2.067 in): 17.43 gallons, weighing about 145 lb. If your "2-inch" pipe is a different material or schedule the ID differs — 2″ copper type L measures about 1.985 in inside, PVC Sch 40 matches the steel table — so enter the actual ID for exact numbers.
Why is the inside diameter different from the pipe size?
Nominal Pipe Size is a naming convention, not a measurement. Steel pipe keeps a fixed outside diameter per NPS so fittings interchange, and the schedule (wall thickness) eats into the bore: ½″ Sch 40 measures 0.622 in inside, 2″ measures 2.067 in. This tool ships the true ASME B36.10M inside diameters as presets so the volume comes from real geometry.
How much does the water in a pipe weigh?
Volume × 62.37 lb/ft³ at 60 °F. A 100 ft run of 6″ Sch 40 holds 20.06 ft³ = 1,251 lb of water — over half a ton on the hangers before insulation. The tool reports lb and kg alongside the volume; for hot systems the density drops slightly (about 61.7 lb/ft³ at 120 °F), so the 60 °F figure is mildly conservative.
Does this work for PVC, copper, or PEX pipe?
Yes — switch to custom ID entry and type the actual inside diameter of your pipe. PVC Sch 40 shares the steel B36.10M dimensions, so the presets apply directly; copper tube (type K/L/M) and PEX have their own ID tables, found on the manufacturer datasheet. The volume math V = π(ID/2)²L is identical for every material.
How do I calculate pipe volume in liters?
Enter the ID in mm and the length in metres on the metric toggle: V(m³) = π × (ID/2000)² × L, and liters = m³ × 1,000. A 100 mm ID pipe over 50 m holds π × 0.05² × 50 = 0.3927 m³ = 392.7 L. The tool always shows both unit families, so metric entry still reports gallons.
How much water do I need to add glycol for a hydronic loop?
Sum each pipe size's run length through the tool (plus the boiler, coils, and expansion tank volumes from their datasheets) to get the system volume, then dose glycol to the target percentage by volume — 30% propylene glycol in a 50-gal system means 15 gal of glycol. The per-100-ft chart makes the takeoff quick: measure runs per size, multiply, add.