Find the internal volume, liquid capacity and fluid weight of any pipe run. Pick your material and nominal size and the real inside diameter is looked up for you — because nominal size is not the bore.
The space between two concentric pipes — a carrier inside a casing, or a jacketed line.
Recent calculations appear here.
Litres per metre for Schedule 40 steel/PVC — your current size is highlighted.
In a horizontal pipe these are not the same thing. The curve is the circular-segment relationship.
Add every run in the system to get a total — useful for sizing a flush, a glycol charge or a chemical dose.
Inside diameter is calculated as OD − 2 × wall. Capacity figures are for a completely full pipe of water.
These are nominal published dimensions from the common standards (ASME B36.10M/B36.19M for NPS, ASTM B88 for copper tube, ASTM F876 for PEX). Real pipe carries manufacturing tolerances, and linings, scale or corrosion reduce the bore further. For anything critical, verify against the standard and the manufacturer's data sheet.
Pipe volume is the volume of a cylinder: V = π × r² × L, where r is the internal radius and L is the length. Using diameter instead, V = π × d² × L ÷ 4. For gallons, work in cubic inches and divide by 231; for litres, work in cubic metres and multiply by 1,000.
The step that trips people up is r. Nominal pipe size is not the bore — a "2-inch" Schedule 40 pipe has an outside diameter of 2.375″ and an inside diameter of about 2.067″, holding roughly 0.174 US gallons per foot (2.16 L/m). Use the size selector above and the correct inside diameter is looked up for you.
Choose material, schedule and nominal size — or type the inside diameter, or OD and wall thickness.
Total run in metres, feet or any supported unit. Add up every branch in the system tab.
Pick a fluid so weight comes from real density, and set the fill level and orientation if it isn't running full.
Capacity in eight units, fluid weight, fill time and per-metre figures. Copy, export CSV or print.
These are the exact calculations running inside the tool.
The error that dominates everything else: using the nominal size as the bore. For NPS 2 Sch 40, taking d = 2.000″ instead of 2.067″ understates capacity by about 6.4%. Because volume goes with the square of the diameter, small diameter mistakes become large volume mistakes.
Each solved with the formulas above. Tap Try it to load the numbers.
Note the ID: 2.067″, not 2″. Using 2″ would give 16.32 gal — a 6.4% shortfall, which matters when you are dosing chemical or charging glycol.
Copper nominal size is smaller than both its OD and, confusingly, close to its ID. A ¾″ Type L tube has OD 0.875″ and ID 0.785″.
Same nominal size, very different bore. This is why "¾-inch pipe" is never enough information to compute a volume — the material and standard have to come with it.
Nearly 3.7 tonnes of water in the pipe alone — a figure worth having before you size supports or plan a drain-down.
Quarter depth is not quarter volume. Treating it as 25% would overstate the contents by 28%, which matters for spill estimates and pumping calculations.
Half depth is the one point where depth and volume coincide, by symmetry. Everywhere else they diverge — and the further from the middle, the bigger the gap.
Sprinkler mains often use Sch 10 rather than Sch 40 — the thinner wall gives a noticeably larger bore and about 11% more water than Sch 40 at the same nominal size.
Roughly 0.0449 gal per foot. Handy field rule for 1″ Sch 40: about 4.5 gallons per 100 feet.
Glycol mixes are around 7% denser than water, so a system charge weighs more than a water figure suggests — relevant for both ordering and structural loading.
Line pack matters for pipeline accounting — nearly 13 m³ of product sits in the line before a drop reaches the far end.
Annular volume uses the outer pipe's inside radius and the inner pipe's outside radius — mixing those up is the classic error here.
An idealised figure. Real filling is slower because air has to escape ahead of the fluid, so vent high points before timing anything critical.
Both are "4-inch pipe" with the same 4.5″ OD. The heavier wall costs nearly a tenth of the capacity, which compounds across a large system.
Flow-and-return doubles this — remember to enter both legs, or use the system tab to add every run at once.
Metric PVC is sized by outside diameter, so 50 mm pipe has a 50 mm OD and roughly 47 mm bore depending on pressure class — the opposite convention to NPS.
Vertical is the easy case: fill fraction and volume fraction are identical. Only horizontal pipes need the segment formula, which is why orientation is an input.
Small bores hold surprisingly little — worth checking before you assume a long ½″ run needs a large flush or dose.
This is exactly NPS 2 / DN50 Sch 40. If you can only measure the outside with callipers, this mode gets you there — just remember to subtract the wall twice.
Because volume scales with diameter squared, a 3.2% diameter error becomes a 6.4% volume error. On a 10,000 L system that is 640 litres of glycol you did not order.
What the number means, where the standards differ, and the mistakes that cost real money.
Pipe volume is the internal capacity of a length of pipe — the space available to the fluid inside. Geometrically a pipe is a right cylinder, so the volume is the cross-sectional area of the bore multiplied by the length: V = πr²L. Everything else on this page is either about getting r right or about what to do when the pipe is not running full.
The critical word is internal. The volume that matters is bounded by the inside surface of the pipe wall, so the inside diameter is the only diameter that belongs in the formula. Using the outside diameter includes the wall material as if it were fluid, which overstates capacity — and because area scales with the square of diameter, the error is always larger than it looks.
This is the single most consequential thing to understand, and it is where most published pipe-volume tables quietly go wrong. For NPS steel and PVC pipe, the nominal size is a label, not a measurement. A "2-inch" pipe has an outside diameter of 2.375 inches — fixed for every schedule — and an inside diameter that depends entirely on the wall thickness. In Schedule 40 that bore is 2.067 inches; in Schedule 80 it is 1.939 inches.
So a table that lists "2 inch pipe = 0.163 gallons per foot" has assumed the bore is exactly 2.000 inches. The real Schedule 40 figure is about 0.174 gallons per foot. That is a 6.4% understatement, and it propagates into every downstream number: flush volumes, chemical doses, glycol charges, drain-down times.
Above NPS 14 the convention changes again: the nominal size is the outside diameter (a 16-inch pipe has a 16.000-inch OD). Below that, the nominal size matches neither the OD nor the ID. There is no shortcut here — you have to look the dimension up, which is what the size selector on this page does.
A schedule number is a wall-thickness designation. Because the outside diameter is held constant for a given nominal size — so that fittings, flanges and threading dies interchange — a heavier schedule can only add material inwards. Higher schedule means thicker wall, higher pressure rating, and smaller bore.
The common progression runs Schedule 5, 10, 40, 80, 160 and then XXS (double extra strong). Schedule 40 is the general-purpose default for water and low-pressure service. Schedule 10 is widely used for fire sprinkler mains and stainless process lines where the pressure demand is modest and the weight saving matters. Schedule 80 appears where pressure, mechanical abuse or threading demands more metal.
The capacity difference is not trivial. A 4-inch Schedule 40 pipe has a 4.026-inch bore; the same nominal size in Schedule 80 is 3.826 inches, holding about 9.7% less. Both are called "4-inch pipe" and both take the same fittings.
Different piping materials use entirely different sizing conventions, and mixing them up produces large errors.
| Material | Sized by | Standard | Note |
|---|---|---|---|
| Steel, stainless, PVC, CPVC | NPS + schedule | ASME B36.10M / B36.19M, ASTM D1785 | Nominal matches neither OD nor ID below NPS 14 |
| Copper tube | Nominal + type K/L/M | ASTM B88 | OD = nominal + ⅛″; K thickest, M thinnest |
| PEX | Nominal, SDR-9 | ASTM F876 | Noticeably smaller bore than copper at the same size |
| Metric PVC / HDPE | Outside diameter | ISO 161 / EN 1452 | 50 mm pipe means 50 mm OD — opposite of NPS |
The practical consequence: "¾-inch pipe" is never enough information to compute a volume. A ¾-inch Type L copper tube has a 0.785-inch bore; ¾-inch PEX has a 0.671-inch bore and therefore holds about 27% less per metre. Same label, very different pipe.
When a pipe runs full, volume is straightforward. When it does not, orientation decides the maths, and this is where most calculators stop.
In a vertical pipe the cross-section is always a complete circle, so the fluid column is simply a shorter cylinder. Fill fraction and volume fraction are identical: half the height is half the volume.
In a horizontal pipe the fluid forms a circular segment — a chord cutting across the circle — and the relationship is decidedly non-linear. With internal radius r and fluid depth h, the wetted area is A = r²(θ − sin θ)/2 where θ = 2·arccos((r − h)/r). Filled to a quarter of its diameter, a horizontal pipe holds only 19.55% of its volume. At half depth it is exactly 50%, by symmetry. At three-quarter depth it is 80.45%.
Treating quarter-depth as quarter-volume overstates the contents by about 28%. For sewer and drainage work, spill estimation, or sizing a pump-out, that is the difference between a right answer and a badly wrong one. The chart beside the calculator plots the whole curve.
Weight follows directly from volume: mass = volume × density. Water is the usual default at about 998 kg/m³ at 20 °C, close enough to 1,000 that a litre of water weighing a kilogram is a serviceable field approximation.
Other fluids diverge enough to matter. Diesel is around 840 kg/m³ and petrol about 745, so a fuel line weighs materially less than the same line full of water. Ethylene glycol is about 1,113 kg/m³ and a 50/50 glycol-water mix around 1,070 — roughly 7% heavier than water, which affects both the quantity you order and the load on hangers and supports. Seawater at about 1,025 kg/m³ sits between.
Density also moves with temperature, which is why a chilled-water system and a heating circuit of identical geometry do not weigh quite the same. For most estimating work a room-temperature figure is fine; for precise process work, use the density at operating temperature.
An annulus is the space between two concentric pipes — a carrier pipe inside a casing, the gap in a jacketed or trace-heated line, or the void to be grouted in a bored crossing. Its volume is the difference of two circular areas: V = π(R² − r²)L.
The radii must be chosen carefully, and this is where the mistakes happen. R is the inside radius of the outer pipe — the bore of the casing, not its nominal size or outside diameter. r is the outside radius of the inner pipe — the carrier's OD, not its bore. Using the wrong pair of dimensions is the classic annular-volume error, and it typically produces an answer that is wrong by tens of percent.
Pipe volume is rarely an end in itself. In plumbing and HVAC it sets the flush volume for commissioning, the glycol charge for a closed circuit, and the dead volume that determines how long a tap runs before hot water arrives. In fire protection it gives the water needed to charge a wet system, and the air volume a compressor must handle in a dry one.
In water treatment and process engineering it drives chemical dosing and contact time, since concentration depends on the volume being treated. In pipeline operation the same figure is "line pack" — the inventory sitting in the line, which matters for both accounting and batching. And across all of them it feeds structural work: a 200 m run of 6-inch main holds nearly 3.7 tonnes of water, a load that has to go somewhere.
The dimensions used here come from the recognised standards: ASME B36.10M for welded and seamless wrought steel pipe and B36.19M for stainless, ASTM D1785 for Schedule 40 and 80 PVC, ASTM B88 for seamless copper water tube, and ASTM F876 for PEX tubing. AWWA standards cover municipal water mains, and the ASHRAE Handbook is the usual reference for HVAC system volumes and fluid properties. Volume conversions are exact by definition: one US gallon is exactly 231 cubic inches, one imperial gallon is exactly 4.54609 litres, and one cubic foot is exactly 28.316846592 litres. Where a manufacturer publishes dimensions for a specific product, those take precedence over any general table.
Treat the pipe as a cylinder and use V = π × r² × L, where r is the internal radius and L is the length. Using diameter instead, V = π × d² × L ÷ 4. Always use the inside diameter, not the nominal size or the outside diameter.
No, and assuming it is causes the most common error in pipe volume calculations. For NPS steel and PVC pipe, a nominal 2 inch Schedule 40 pipe has an outside diameter of 2.375 inches and an inside diameter of about 2.067 inches. For copper tube the nominal size is smaller than both. Look up the real inside diameter for your material and schedule.
A 2 inch Schedule 40 pipe has an inside diameter of about 2.067 inches, so it holds roughly 0.174 US gallons per foot, or about 2.16 litres per metre. Over a 100 foot run that is about 17.4 US gallons.
Work out the volume in cubic inches with π × r² × L, then divide by 231 because one US gallon is exactly 231 cubic inches. For litres, calculate the volume in cubic metres and multiply by 1,000.
Multiply the internal volume by the fluid density: mass = volume × density. Water at 20 °C is about 998 kg/m³, so a pipe holding 0.5 m³ of water contains roughly 499 kg.
For a horizontal pipe the wetted cross section is a circular segment, not a simple percentage. With internal radius r and fluid depth h, the area is r²(θ − sin θ)/2 where θ = 2·arccos((r − h)/r). A horizontal pipe filled to a quarter of its depth holds about 19.6% of its volume, not 25%. For a vertical pipe the relationship is linear.
It is the volume of the space between two concentric pipes, such as a carrier pipe inside a casing or the gap in a jacketed line. Calculate it as π × (R² − r²) × L, where R is the outer pipe's inside radius and r is the inner pipe's outside radius.
Divide the internal volume by the flow rate, keeping units consistent. A pipe holding 200 litres filled at 20 litres per minute takes 10 minutes. The same method gives drain time if you know the drain rate.
Always the inside diameter, because that is the space the fluid occupies. If you only know the outside diameter, subtract twice the wall thickness. Using the outside diameter overstates capacity, and the error grows quickly on thick-walled or small-bore pipe.
A 1 inch Schedule 40 pipe has an inside diameter of about 1.049 inches, giving roughly 0.0449 US gallons per foot, so 100 feet holds about 4.5 US gallons or 17 litres.
Yes, because different materials use different wall thicknesses at the same nominal size. A ¾ inch copper Type L tube has an inside diameter of about 0.785 inches while ¾ inch PEX is about 0.671 inches, so the copper holds noticeably more per metre.
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Schedule 80 has a thicker wall for the same outside diameter, so it withstands more pressure but has a smaller bore. At 4 inch nominal, Sch 40 has a 4.026 inch bore and Sch 80 has 3.826 inches — about 9.7% less capacity from pipe that looks identical from outside.
If the bore is genuinely 100 mm, it holds 7.854 litres per metre. But a "100 mm" pipe often means DN100 / NPS 4, whose Schedule 40 bore is 102.26 mm, giving 8.21 L/m. Check whether your 100 mm refers to the nominal size or the actual inside diameter.
Convert the radius and length to feet first, then apply π × r² × L. Alternatively compute in cubic inches and divide by 1,728, since there are 12³ cubic inches in a cubic foot.
No. A US gallon is exactly 231 cubic inches (3.785 litres) while an imperial gallon is exactly 4.54609 litres — about 20% larger. The calculator shows both, so check which one your specification means.
The geometric volume barely changes — thermal expansion of the pipe wall is a fraction of a percent over normal ranges. What does change is the fluid: density falls as temperature rises, so the same pipe holds the same volume but a slightly different mass. Use the density at operating temperature for precise work.
For most estimating, measure the total centre-line run and treat fittings as pipe — the error is small. Where accuracy matters, add manufacturer volumes for large valves, strainers and vessels separately, since these can hold far more than the equivalent length of pipe.
Usual causes are the bore being reduced by scale, lining or corrosion in older pipework; missing branches or a forgotten return leg; vessels, coils and valves not counted; or air pockets at high points. Manufacturing tolerance also means real pipe varies slightly from published dimensions.
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Pipe dimensions are set by standards bodies and manufacturers; the links below are authoritative starting points.
This Pipe Volume Calculator provides engineering estimates based on the dimensions, pipe schedule, material and fluid properties you enter. Actual pipe capacities may vary depending on manufacturing tolerances, fittings, valves and installation conditions. Always verify dimensions and specifications using applicable engineering standards and manufacturer documentation.