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Calculate the volume of any pipe in litres, gallons, or cubic metres. Works for water pipes, heating systems, gas installations, and industrial pipelines.
Knowing the volume of a pipe is one of the most practical calculations in plumbing, heating, and gas engineering. Whether you need to know how many litres of water are in a central heating system, how much fluid a pipeline holds before commissioning, or the installation volume of a gas pipework system for purge calculations, the same core formula applies.
This page gives you a free, instant pipe volume calculator plus the full formula, unit conversions, copper pipe volume charts, a dedicated gas installation volume guide, and worked examples covering domestic plumbing to large-bore pipelines.
Enter the pipe's internal diameter and length. Select your preferred units and click Calculate. Results are shown in litres, UK gallons, and cubic metres simultaneously.
A pipe is simply a hollow cylinder. The pipe volume formula is the standard cylinder volume formula applied to the internal bore:
Where:
You can also write this using the diameter directly:
The formula gives you cubic units. To convert to useful real-world units:
| Input units | Result in | To get litres | To get UK gallons | To get m³ |
|---|---|---|---|---|
| millimetres (mm) | mm³ | ÷ 1,000,000 | ÷ 4,546,090 | ÷ 1,000,000,000 |
| centimetres (cm) | cm³ | ÷ 1,000 | ÷ 4,546.09 | ÷ 1,000,000 |
| metres (m) | m³ | × 1,000 | × 219.969 | × 1 |
| inches (in) | in³ | × 0.016387 | × 0.003605 | × 0.000016387 |
| feet (ft) | ft³ | × 28.3168 | × 6.2288 | × 0.028317 |
The tables below give you pre-calculated volumes for the most common pipe sizes used in the UK and internationally. All values use the typical internal diameter for each nominal size.
Standard UK copper pipe (to EN 1057). Internal diameters are approximate; actual IDs vary slightly by manufacturer and grade.
| Nominal OD (mm) | Typical ID (mm) | Wall (mm) | L per metre | mL per metre | UK gal / metre | US gal / foot | m³ per 10m |
|---|---|---|---|---|---|---|---|
| 6 mm | 4.0 mm | 1.0 | 0.013 | 12.6 | 0.0028 | 0.00034 | 0.000126 |
| 8 mm | 6.0 mm | 1.0 | 0.028 | 28.3 | 0.0062 | 0.00075 | 0.000283 |
| 10 mm | 8.0 mm | 1.0 | 0.050 | 50.3 | 0.0111 | 0.00133 | 0.000503 |
| 15 mm | 13.0 mm | 1.0 | 0.133 | 132.7 | 0.0292 | 0.00351 | 0.001327 |
| 22 mm | 20.0 mm | 1.0 | 0.314 | 314.2 | 0.0691 | 0.00831 | 0.003142 |
| 28 mm | 26.0 mm | 1.0 | 0.531 | 530.9 | 0.1168 | 0.01405 | 0.005309 |
| 35 mm | 32.6 mm | 1.2 | 0.835 | 835.2 | 0.1836 | 0.02210 | 0.008352 |
| 42 mm | 39.6 mm | 1.2 | 1.231 | 1231 | 0.2708 | 0.03258 | 0.01231 |
| 54 mm | 51.6 mm | 1.2 | 2.093 | 2093 | 0.4603 | 0.05540 | 0.02093 |
| 67 mm | 64.0 mm | 1.5 | 3.217 | 3217 | 0.7078 | 0.08516 | 0.03217 |
| 76 mm | 73.0 mm | 1.5 | 4.185 | 4185 | 0.9206 | 0.11077 | 0.04185 |
For commercial and industrial applications. Internal diameter is taken as OD minus a typical wall thickness; verify your specific pipe schedule or standard.
| Nominal size | Approx ID (mm) | L per metre | UK gal / metre | m³ per 100m | m³ per 1 km |
|---|---|---|---|---|---|
| 100 mm (4 in) | 98 mm | 7.54 | 1.659 | 0.754 | 7.54 |
| 150 mm (6 in) | 147 mm | 16.97 | 3.733 | 1.697 | 16.97 |
| 200 mm (8 in) | 196 mm | 30.17 | 6.637 | 3.017 | 30.17 |
| 250 mm (10 in) | 246 mm | 47.52 | 10.453 | 4.752 | 47.52 |
| 300 mm (12 in) | 296 mm | 68.83 | 15.143 | 6.883 | 68.83 |
| 400 mm (16 in) | 394 mm | 121.9 | 26.81 | 12.19 | 121.9 |
| 500 mm (20 in) | 493 mm | 191.0 | 42.02 | 19.10 | 191.0 |
| Nominal OD (mm) | Typical ID (mm) | Material | L per metre | UK gal / metre |
|---|---|---|---|---|
| 20 mm | 16.2 mm | MDPE (water) | 0.206 | 0.0453 |
| 25 mm | 20.4 mm | MDPE (water) | 0.327 | 0.0719 |
| 32 mm | 26.2 mm | MDPE | 0.539 | 0.1186 |
| 20 mm | 15.3 mm | PVC Class C | 0.184 | 0.0405 |
| 32 mm | 27.0 mm | PVC Class C | 0.573 | 0.1260 |
| 40 mm | 34.4 mm | PVC Class C | 0.929 | 0.2044 |
| 50 mm | 43.4 mm | PVC Class C | 1.480 | 0.3256 |
| 110 mm | 103.6 mm | PVC soil/drain | 8.430 | 1.855 |
| Nominal pipe size | OD (mm) | ID Sch 40 (mm) | L per metre | UK gal/ft | US gal/ft |
|---|---|---|---|---|---|
| ½ in | 21.3 | 15.8 | 0.196 | 0.0132 | 0.0158 |
| ¾ in | 26.7 | 20.9 | 0.343 | 0.0231 | 0.0278 |
| 1 in | 33.4 | 26.6 | 0.556 | 0.0374 | 0.0450 |
| 1½ in | 48.3 | 40.9 | 1.314 | 0.0884 | 0.1064 |
| 2 in | 60.3 | 52.5 | 2.165 | 0.1457 | 0.1753 |
| 3 in | 88.9 | 77.9 | 4.767 | 0.3208 | 0.3862 |
| 4 in | 114.3 | 102.3 | 8.213 | 0.5527 | 0.6651 |
| 6 in | 168.3 | 154.1 | 18.66 | 1.2566 | 1.5118 |
Calculating the volume of water in a pipe is essential for several practical tasks:
When you're sizing a heating system, you need to know the total water volume to correctly size the expansion vessel, determine the correct inhibitor dosage, and calculate chemical flush volumes. A typical UK domestic system holds 8–15 litres in the pipework alone, plus the boiler heat exchanger and radiators.
Powerflush contractors and plumbers need to know the total water volume to dose inhibitor, cleaner, or biocide at the correct concentration. Under-dosing leaves systems vulnerable to corrosion and scale; over-dosing wastes money and can affect system components.
Knowing how much water a pipe or pipeline holds lets you estimate filling time at a given flow rate. It also informs hydraulic calculations: a full pipe under pressure exerts more force than engineers might assume if they overlook the water mass.
In commercial and industrial settings, dead-legs (pipe sections that see infrequent flow) can accumulate stagnant water. Legionella risk assessments require accurate pipe volume data for every section of a building's hot and cold water system.
Gas engineers need to calculate the installation volume of pipework for two key purposes: gas tightness testing and gas purging calculations. Both are Gas Safe requirements under IGEM/UP/1B and the Gas Safety (Installation and Use) Regulations 1998.
Gas installation volume is the total internal volume of all the pipework and components in a gas installation, measured in cubic metres (m³) or litres. It includes every pipe section from the outlet of the emergency control valve (ECV) to the appliance connections, plus the volume of meters, governors, flexible connections, and any other components within the installation.
Sum the volume of each pipe section using the standard cylinder formula:
Then add the volume of the gas meter (typically stamped on the meter or available from the meter data sheet) and any other in-line components.
Scenario: 3-bedroom semi-detached house
When introducing gas to a new or recommissioned installation, the pipework must be purged of air. The purge volume required depends on the total installation volume. For installations below 0.035 m³ (35 litres), the standard purge procedure under IGEM/UP/1B applies. Larger installations require a different approach.
Gas Safe requirement: All gas work must be carried out by a Gas Safe registered engineer. Installation volume calculations affect the tightness testing pressure decay limits. Always verify calculations against current IGEM/UP/1B guidance and your employer's procedures.
Under the let-by test and tightness test procedures, the acceptable pressure drop depends on the installation volume. A larger volume means a smaller pressure drop is acceptable for a given leak rate. Gas engineers must know the installation volume to determine the correct pass/fail criterion for the test gauge reading after the stabilisation period.
| Material | Nominal size | OD (mm) | Typical ID (mm) | L per metre |
|---|---|---|---|---|
| Copper (EN 1057) | 10 mm | 10 | 8.0 | 0.0503 |
| Copper (EN 1057) | 15 mm | 15 | 13.0 | 0.1327 |
| Copper (EN 1057) | 22 mm | 22 | 20.0 | 0.3142 |
| Copper (EN 1057) | 28 mm | 28 | 26.0 | 0.5309 |
| Steel (BS 1387) | ½ in BSP | 21.3 | 15.8 | 0.1961 |
| Steel (BS 1387) | ¾ in BSP | 26.7 | 20.9 | 0.3431 |
| Corrugated SS (CSST) | DN15 | — | ~13.5 | ~0.143 |
| PE/yellow MDPE | 32 mm | 32 | 26.2 | 0.539 |
These two terms are often used interchangeably, but they describe slightly different things:
For filling calculations (how long to fill a pipeline), you use the static volume. For sizing calculations (will this pipe deliver enough flow?), you need the hydraulic capacity and flow rate. See our pipe flow rate calculator for flow and velocity calculations.
The hydraulic capacity of a pipe is influenced by its internal diameter (the most important factor), wall roughness, fluid velocity, and pressure. Doubling the diameter increases the flow capacity by a factor of four, because the cross-sectional area — and therefore the volume it can carry — increases with the square of the diameter.
The volume a pipe holds depends entirely on its internal diameter, not the nominal size marked on the outside. Different materials and pipe standards result in different wall thicknesses, which means the internal diameter varies even between pipes of the same nominal size.
UK copper pipe is made to EN 1057. The most common type (Table X, or R250) has a wall thickness of about 0.7–1.5mm depending on diameter. A nominal 15mm copper pipe has an outside diameter of exactly 15mm and an internal diameter of approximately 13mm. Always check the manufacturer's datasheet for the exact internal diameter if precision matters.
PVC pipe comes in several pressure classes (Class C, Class D, Class E for cold water service) and each class has a different wall thickness for the same outside diameter. Class C (lower pressure) has a thinner wall and therefore a larger internal volume than Class E (higher pressure). The nominal OD is fixed; the ID varies by class.
Steel pipe uses a "schedule" system where the schedule number determines wall thickness. Schedule 40 is the most common. A 2-inch Schedule 40 steel pipe has an ID of 52.5mm; the same pipe in Schedule 80 has an ID of 49.3mm — a meaningful difference for accurate volume calculations.
MDPE pipe, commonly used for underground water mains and gas supplies in the UK, is sized by outside diameter. The SDR (standard dimension ratio) determines the wall thickness. Blue MDPE (water) and yellow MDPE (gas) often share the same outside diameter but may have different wall specifications. Always use manufacturer data for internal diameter.
Use these tools alongside the pipe volume calculator for complete plumbing, heating, and gas system design: