Pipe Volume Calculator

Written byOleh Soloninupdated 27 September 2026

Internal diameter, mm

External diameter, mm

Length, m

Material

Advanced options

Material density, kg/m³

0 takes the density of the chosen material: polypropylene 920, PVC 1390, steel 7860, copper 8920 kg/m³.

Result

Volume, litres15.71
Volume, m³0.01571
Litres per metre0.314
Surface area, m²3.93
Pipe mass, kg8.13
Wall thickness2.5 mm
How it was calculated
π × (20 ÷ 2000)² × 50 = 0.01571 m³, that is 15.71 litres per metre: 0.314 litres wall: π × ((25 ÷ 2000)² − (20 ÷ 2000)²) × 50 × 920 kg/m³ = 8.13 kg

For expansion vessels and for lagging

How much water a pipe holds, litres per metre, external surface area and the mass of the pipe itself.

The volume of a pipe is the area of the circle times the length. A polypropylene pipe with a 20 mm bore holds 15.71 litres over 50 metres — 0.314 litres per metre. That is what drains out when the system is emptied, and what has to be heated when it is filled again.

The second figure is the weight of the pipe itself: the volume of the wall times the density of the material. For that same 20 × 25 mm pipe it is 8.13 kg; for a steel 100 × 108 mm pipe over 12 metres, 123.27 kg, because steel is eight and a half times denser than polypropylene.

How to use

Enter the inside and outside diameters in millimetres and the length in metres.
Pick the material — its density is applied automatically; override it if your pipe differs.
Read the volume in litres, the litres per metre, the wall thickness, the weight and the surface area.

Litres and weight for common sizes

Every row is a separate run of this calculator with the density of the chosen material.

Every value was produced by the calculator on this page.
Pipe	Length	Wall	Volume	Per metre	Weight	Surface
Polypropylene 20 × 25 mm	50 m	2.5 mm	15.71 l	0.314 l	8.13 kg	3.93 m²
Polypropylene 15 × 20 mm	30 m	2.5 mm	5.3 l	0.177 l	3.79 kg	1.88 m²
PVC 32 × 40 mm	25 m	4 mm	20.11 l	0.804 l	15.72 kg	3.14 m²
Steel 100 × 108 mm	12 m	4 mm	94.25 l	7.854 l	123.27 kg	4.07 m²
Copper 20 × 22 mm	15 m	1 mm	4.71 l	0.314 l	8.83 kg	1.04 m²

The densities behind the weights

Steel 7,860 kg/m³ and copper 8,920 kg/m³ come from the Russian Wikipedia articles on steel (ρ ≈ 7.86 g/cm³) and copper (8.92 g/cm³); polypropylene 920 kg/m³ from the article on polypropylene (0.92–0.93 g/cm³); PVC 1,390 kg/m³ from the article on polyvinyl chloride (1.39 ± 0.04 g/cm³).

If your pipe is different — glass-fibre reinforced polypropylene, for instance — enter the density by hand and the weight follows.

Diameter beats length

Volume grows with the square of the bore: 15 mm holds 0.177 litres per metre, 20 mm holds 0.314 and 100 mm already holds 7.854. In a heating system most of the water therefore sits in the mains and the emitters, not in the branches.

The wall thickness is printed separately: it is half the difference between the diameters. For a 20 × 25 mm pipe that is 2.5 mm, for a copper 20 × 22 mm pipe 1 mm — and it is what sets the weight and the pressure rating.

What this calculator shows

Volume in litres and cubic metres, plus litres per metre
External surface area for insulation and painting
The pipe's own mass for the material selected

What to keep in mind

Volume uses the internal diameter: polypropylene has thick walls, and the gap to the external diameter reaches a third.
Densities are the reference values: steel 7,860, copper 8,920, polypropylene 920, PVC 1,390 kg/m³.

FAQs

How many litres in a metre of 20 mm pipe?

0.314 litres for a 20 mm bore: a cross-section of 3.14 cm² over a metre. Fifty metres hold 15.71 litres.

How do I work out the water content of a heating system?

Add up the sections of pipe and then the volume of the emitters and the boiler. This page does the sections: bore, length and material.

How much does a steel pipe weigh?

Wall volume times density. A 100 × 108 mm pipe 12 m long weighs 123.27 kg at 7,860 kg/m³; the same geometry in polypropylene would be about 14 kg.

Why would I need the surface area?

For the heat a bare pipe gives off, for paint and for insulation. A 25 mm pipe over 50 metres has 3.93 m² of surface.

Is the marked size the bore or the outside diameter?

Polypropylene and multilayer pipes are marked by outside diameter; threaded steel pipe by nominal bore, which matches neither the actual bore nor the outside. Volume depends only on the bore, which is why there are two fields.

What is the wall thickness?

Half the difference between the outside and inside diameters: 2.5 mm for a 20 × 25 mm pipe. The calculator prints it and refuses an outside diameter smaller than the bore.

Worked example

A 50-metre circuit

Input: 20 mm bore, 25 mm outside, 50 m, polypropylene

Output: 15.71 litres, 0.314 litres per metre, 8.13 kg

Note: The surface area, 3.93 m², is what heat loss and insulation are calculated from.

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