Room Volume Calculator — m³, Litres & Cubic Feet
Calculate room volume in cubic metres (m³), litres and cubic feet from length, width and height. Free UK room volume calculator for building and heating estimates.
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How to calculate room volume
For a simple rectangular room, multiply the internal length × internal width × internal height, with all three measurements in metres. The result is the room volume in cubic metres (m³).
Worked example: 5 m × 4 m × 2.4 m
What room measurements should you use?
Use the internal dimensions of the space whose air volume you want to estimate. Measure actual room length and width rather than relying on nominal plan dimensions where accuracy matters. For a flat ceiling, use the internal floor-to-ceiling height.
If you need only the floor area, use the Floor Area Calculator. If you are calculating a generic solid or material volume rather than a room, use the Cubic Metre Calculator.
Sloping, vaulted and irregular ceilings
A single average height can give a rough planning figure, but irregular rooms are better split into simpler shapes. For a room with a sloping ceiling, calculate the main rectangular volume and any triangular or additional sections separately where practical, then add the volumes together.
Flat ceiling
Length × width × height is normally sufficient for a simple rectangular room.
Sloping ceiling
Use an average height only for a rough estimate. Split the geometry into simpler sections when the result needs to be more accurate.
Open-plan or linked spaces
Measure each distinct section and add the volumes if the space cannot be represented reliably by one rectangle.
Room volume and heating calculations
Room volume can be one input in some heating, ventilation or air-change calculations, but volume alone does not determine heat loss or radiator size. Building fabric, insulation, glazing, air leakage, ventilation, design temperatures and other factors also matter. Do not treat this page as a heat-loss calculator.
Room volume and air-change calculations
If you are using room volume as part of a ventilation or air-change calculation, keep the units explicit. This tool gives volume only; it does not determine the ventilation rate required for a particular room or building use.
Common room-volume mistakes
- Using external building dimensions instead of the internal room dimensions.
- Mixing centimetres or millimetres with metres before multiplying.
- Ignoring a significant sloping or vaulted section.
- Confusing floor area in m² with room volume in m³.
- Using room volume alone to size heating or ventilation equipment.
Useful conversions
1 m³ = 1,000 litres. The calculator also converts to cubic feet automatically. If your source dimensions are imperial, convert them first with the Length Converter so all three inputs use compatible units.
Planning measurement only. This tool calculates geometric room volume. It does not verify heating loads, ventilation rates, occupancy requirements or regulatory compliance.
Frequently asked questions
How do I calculate the cubic metres of a room?
Multiply the room length by the room width by the internal height, with all three measurements in metres.
How many litres are in a cubic metre?
One cubic metre equals exactly 1,000 litres.
How do I calculate room volume with a sloping ceiling?
For a rough estimate you can use an average height. For better accuracy, split the room into simpler geometric sections and add their volumes.
Is room volume the same as floor area?
No. Floor area is measured in square metres (m²), while room volume includes height and is measured in cubic metres (m³).
Can room volume tell me what radiator size I need?
No. Proper heat-loss calculations also need information about insulation, walls, windows, ventilation and design temperatures.
Can I use this for ventilation calculations?
You can use the room volume as an input, but the calculator does not determine the required ventilation or air-change rate.
Related measuring tools
For floor or wall geometry, use the Floor Area Calculator or Wall Area Calculator. For all measurement and conversion tools, return to the Measuring & Conversions hub.