Example 1
- Length: 5 m
- Width: 4 m
- Height: 2.5 m
Volume: 50 m³
What volume is a 5×4×2.5 m room? 5×4×2.5 = 50 m³.
Room Volume Calculator
Enter length, width, and height. The calculator multiplies three sides, subtracts a deduction, and multiplies by repeats. A 5 × 4 × 2.5 m room is 50 m³. A 6 × 5 × 2.8 m living room is 84 m³. It also shows floor area and a 40 W/m³ heating estimate.
Results
Enter length, width, and height; a volume deduction is optional. Room volume appears below.
Room volume is the space inside — useful for air changes, heating load, and comparing rooms with the same floor but different height. Related: heating power, wall area, floor area.
How the results are calculated
Length5 m
Width4 m
Height2.5 m
Volume50 m³
The room volume calculator counts cubic meters inside the room. The formula is max(0, length × width × height − deduction) × repeat count. The heating estimate is about 40 W/m³ times a type factor: bathroom 1.2, attic 1.1, standard 1.0. This is geometry plus a quick estimate, not an energy audit.
A living room 5 × 4 × 2.5 m is 50 m³. At 40 W/m³ the estimate is 2000 W, or 2.00 kW. A 6 × 5 × 2.8 m living room is 84 m³. A 3.5 × 3 × 2.6 m bedroom is 27.3 m³. Floor area at 5 by 4 m is 20 m².
Enter length, width, and height in the header unit. Leave deduction, room type, and repeats empty when you count one ordinary room. An empty deduction subtracts nothing.
Heating power from this volume lives on the heating page. Walls 4 × 3 × 2.6 m are 36.4 m² on the wall area page. Floor area 5 × 4 m lives on the floor area page, without height.
The same 20 m² floor at 2.5 m height is 50 m³; at 2.8 m it would be 56 m³. A roof slope is not automatic: enter an average height or subtract dead volume. Bathroom type raises only the watt estimate.
Enter 5, 4, and 2.5, click Calculate, and match 50 m³. Then 6, 5, and 2.8: 84 m³.
How to use this calculator
- Enter length, width, and height in the header unit, for example 5, 4, and 2.5.
- Optionally deduct volume, for example a cabinet you do not heat.
- Leave room type and repeat count empty when you count one ordinary room.
- Click Calculate. 5×4×2.5 m gives 50 m³. 6×5×2.8 m gives 84 m³.
- Refine watts on the heating page. Here you keep m³ and a quick estimate.
Formula
volume = max(0, length × width × height − deduction) × repeats
heating estimate ≈ volume × 40 W/m³ × type_factor
Factors: standard 1.0 · bathroom 1.2 · attic 1.1. At 5 × 4 × 2.5 m: 5 × 4 × 2.5 = 50 m³. At 40 W/m³ the estimate is 2000 W (2.00 kW). Floor area for those sides is 20 m². This is geometry plus a quick estimate, not an energy audit.
m³ from three sides
Room volume: 5×4×2.5 m is 50 m³. A 6×5×2.8 m living room is 84 m³. A 3.5×3×2.6 m bedroom is 27.3 m³.
- m³
- Interior volume. 50 from a 5×4×2.5 m room. 84 from the living room. Use that figure with W/m³ on the heating page.
- m²
- Floor area = length × width. At 5 by 4 m that is 20 m², without height.
- W
- Heating estimate. 50 m³ × 40 W/m³ = 2000 W. Bathroom type only scales that estimate.
- deduct
- Dead volume before repeats. At 3×5×4 m minus 2.7 m³ the result is 57.3 m³.
Example scenarios
Example 2
- Length: 6 m
- Width: 5 m
- Height: 2.8 m
Volume: 84 m³
A 6×5×2.8 m living room → 84 m³. Floor area alone (30 m²) hides the height.
Example 3
- Length: 3.5 m
- Width: 3 m
- Height: 2.6 m
Volume: 27.3 m³
A 3.5×3×2.6 m bedroom → 27.3 m³.
Example 4
- Length: 3 m
- Width: 5 m
- Height: 4 m
- Deduct volume: 2.7 m³
Volume: 57.3 m³
A 2.7 m³ deduction comes off the 60 m³ gross box. Net volume before repeats is 57.3 m³.
Example 5
- Length: 2.4 m
- Width: 1.6 m
- Height: 2.5 m
- Room type: bathroom
Volume: 9.6 m³
Volume stays 9.6 m³. The bathroom type only scales the 40 W/m³ heat estimate to about 461 W.
Example 6
- Length: 3.5 m
- Width: 3 m
- Height: 2.6 m
- Repeat count: 2
Volume: 54.6 m³
Two matching bedrooms use one set of sides and a repeat count of 2, so 27.3 × 2 = 54.6 m³.
Related calculators
Frequently asked questions
How do I calculate room volume from length, width, and height?
Multiply the three sides, subtract an optional deduction, and multiply by the repeat count. A 5×4×2.5 m room → 50 m³. A 6×5×2.8 m living room → 84 m³.
What is the volume of a 5×4 m room at 2.5 m height?
50 m³. Floor area is 20 m²; volume multiplies that by height. A 3.5×3×2.6 m bedroom is 27.3 m³.
Is this floor area or whole-building volume?
No. Here you get the volume of one rectangular room (or repeats of it). Floor area and whole-building volume are separate topics.
Does the result replace a heating-power calculator or energy audit?
No. It reports m³ and a rough 40 W/m³ hint. Full heating power lives on a separate card; an energy audit is outside this tool.
Is this a free room volume calculator?
Yes. Enter three sides (plus optional deduction and repeats) and you see cubic meters at once. No account required.
How is room volume calculated?
The calculator multiplies length, width, and height, subtracts an optional deduction, and multiplies by the repeat count. At 5 × 4 × 2.5 m the result is 50 m³. At 6 × 5 × 2.8 m the result is 84 m³.
How is volume different from floor area?
Floor area is length × width. At 5 by 4 m that is 20 m². Volume multiplies that by height. At 2.5 m the result is 50 m³.
What do deduct volume and repeat count do?
Deduct removes dead volume (for example a cabinet you do not heat). Repeats multiply the result for several identical rooms. An empty deduction subtracts nothing.
What do bathroom and attic types do?
They do not change the volume itself. The heating estimate multiplies 40 W/m³ by 1.2 (bathroom) or 1.1 (attic). At 50 m³ with the standard type that is about 2000 W.
Does a roof slope enter the formula?
The formula uses a rectangular box. With a slope, enter an average height or subtract dead volume in the deduction field.
Where do I calculate heating power from this volume?
On the heating power page. At 50 m³ and 40 W/m³ the result is 2000 W (2.00 kW). Here the calculator reports cubic meters and a quick watt estimate.
How do I count two identical rooms?
Enter one room’s dimensions and set the repeat count to 2. Or add volumes separately and leave one room here.
What if the deduction is larger than L×W×H?
The result does not go below zero. The calculator uses max(0, L×W×H − deduction), then multiplies by repeats.
Do header units change the formula?
Only the conversions. In meters the result is m³. With feet selected the result is ft³. The formula stays the product of three sides.
Does the result replace an energy audit?
No. It is room geometry plus a simple 40 W/m³ estimate. Insulation, windows, and location need a separate review. The calculator reports volume.
Knowledge sources
Room volume follows from the volume of a rectangular box. Below are volume and SI units.
Page updated October 12, 2026.