Example 1
- Volume: 50 m³
- Heat demand: 40 W/m³
Heating power: 2000 W
That is about 2.00 kW
How many watts for 50 m³ at 40 W/m³? 50×40 = 2000 W (2.00 kW).
Heating Power Calculator
Enter volume in m³ and a W/m³ demand figure. The calculator multiplies them into watts and shows kilowatts. A 50 m³ room at 40 W/m³ is 2000 W (2.00 kW). An 84 m³ living room at 35 W/m³ is 2940 W. Optionally it applies a room factor and window add-on.
Results
Room volume (m³), Heat demand (W/m³), Building standard (auto W/m³) and Room type. The result shows up here.
The heating calculator gives a quick power estimate from room volume and a W/m³ figure. It does not replace a full heat-loss calculation. Related: room volume, insulation.
How the results are calculated
Volume50 m³
Demand40 W/m³
Power2000 W
The heating calculator counts power from room volume. The formula is m³ × W/m³ × room factor, plus 100 W for each m² of windows. Kilowatts are watts divided by 1000. Building standard can fill the demand figure when W/m³ is empty.
A 50 m³ room at 40 W/m³ is 2000 W, or 2.00 kW. An 84 m³ living room at 35 W/m³ gives 2940 W. A 27.3 m³ bedroom at 45 W/m³ is 1228.5 W, about 1.23 kW. Those volumes come from the room volume calculator: 5×4×2.5, 6×5×2.8, and 3.5×3×2.6 m.
Enter volume and demand in W/m³, or pick a building standard. Leave room type and windows empty when a simple volume × W/m³ estimate is enough. A comma in 27.3 works like 27.3.
Compute 50 m³ on the room volume page. Insulation of 120 m² at a 60×120 cm board and 8% is 181 boards and R about 4.17 — a separate calculation; this page keeps power in W and kW.
This is an estimate, not a heat-loss design. An older house is often nearer 45–50 W/m³; a newer one nearer 30–35. Empty windows add nothing. A bathroom at 50 m³ and 40 W/m³ raises the result to 2400 W.
Enter 50 and 40, click Calculate, and match 2000 W and 2.00 kW. Then 84 and 35: 2940 W. Finally 27.3 and 45: 1228.5 W.
How to use this calculator
- Enter volume in m³, for example 50 from a 5×4×2.5 m room.
- Enter demand in W/m³, for example 40, or pick a building standard.
- Leave room type and window area empty when a simple volume × W/m³ estimate is enough.
- Click Calculate. 50 m³ and 40 W/m³ give 2000 W, about 2.00 kW.
- Compute volume on the room volume page. Here you keep watts and kilowatts.
Formula
power_W = volume_m³ × W/m³ × room_factor + windows_m² × 100
power_kW = power_W ÷ 1000
Factors: living 1.0 · bathroom 1.2 · attic 1.1. At 50 m³ and 40 W/m³: 50 × 40 = 2000 W (2.00 kW). An 84 m³ living room at 35 W/m³ gives 2940 W. This is a quick estimate, not a heat-loss design.
kW from 50 m³ at 40 W/m³
Volume times demand. A 50 m³ room at 40 W/m³ is 2000 W, about 2.00 kW.
- kW
- Power in kilowatts. 2000 W is 2.00 kW. An 84 m³ living room at 35 W/m³ is 2940 W, about 2.94 kW.
- W/m³
- Demand from the field or from building standard. 40 on 50 m³ gives 2000 W. 45 on a 27.3 m³ bedroom is 1228.5 W.
- m³
- Volume from the room volume calculator. 50 m³ at 40 W/m³ is that 2.00 kW, not floor area alone.
- windows
- Optional add-on of 100 W per m². At 4 m² on a 2000 W base the result is 2400 W.
Example scenarios
Example 2
- Volume: 84 m³
- Heat demand: 35 W/m³
Heating power: 2940 W
That is about 2.94 kW
An 84 m³ living room at 35 W/m³ → 2940 W (2.94 kW).
Example 3
- Volume: 27.3 m³
- Heat demand: 45 W/m³
Heating power: 1228.5 W
That is about 1.23 kW
27.3 m³ at 45 W/m³ → 1228.5 W (1.23 kW).
Related calculators
Frequently asked questions
How do I calculate heating power from room volume and W/m³?
Multiply volume by W/m³, then by the room factor, and add windows × 100 W/m². 50 m³ × 40 W/m³ → 2000 W (2.00 kW).
How many watts do 50 m³ at 40 W/m³ need?
2000 W, or 2.00 kW. An 84 m³ living room at 35 W/m³ is 2940 W. Get the 50 m³ volume on the room-volume card.
Is this a BTU calculator for air conditioning?
No. This page reports watts and kilowatts from volume and W/m³. AC BTU sizing and a full heat-loss design are outside this tool.
Does the result replace a heating design or energy audit?
No. It is a shopping estimate from a simple rule of thumb. Insulation, bridges, and boiler selection need a project.
Is this a free heating power calculator?
Yes. Enter volume and W/m³ (plus optional room type and windows) and you see watts at once. No account required.
How is heating power calculated?
The calculator multiplies volume by W/m³, then by the room factor, and adds windows (100 W per m²) when you enter them. At 50 m³ and 40 W/m³ the result is 2000 W, or 2.00 kW.
What does the W/m³ figure mean?
It is an approximate power demand per cubic meter. 40 W/m³ is a common starting point. An older building is often nearer 45–50; a newer one nearer 30–35. Building standard can fill that number.
How does building standard work?
When the W/m³ field is empty, the calculator uses the standard: new ~30, well insulated ~40, average ~60, old ~90. When W/m³ is filled, the standard does not overwrite it.
What does room type do?
It multiplies base power. Living = 1.0, bathroom = 1.2, attic = 1.1. At 50 m³ and 40 W/m³ a bathroom gives 2400 W instead of 2000 W.
How are windows counted?
Each m² of windows adds 100 W after the room factor. An empty window field adds nothing. At 50 m³, 40 W/m³, and 4 m² of windows the result is 2400 W.
Where do I get a 50 m³ volume?
From the room volume calculator: 5 × 4 × 2.5 m = 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.
Does the result show watts and kilowatts?
Yes. Watts are the primary result; kilowatts sit beside them. 2000 W is 2.00 kW. 2940 W is 2.94 kW. 1228.5 W is about 1.23 kW.
Does insulation change this result?
Not on this page. Insulation counts boards and R. Here you keep W = m³ × W/m³ (plus optional multipliers). Better insulation may justify a lower W/m³ figure.
Does a comma in 27.3 m³ work?
Yes. 27.3 and 27,3 are the same volume. At 45 W/m³ the result is 1228.5 W, about 1.23 kW.
Does the result replace a heating design?
No. It is a quick estimate from volume and a demand figure. Heat loss, bridges, and ventilation need a separate review. The calculator reports W and kW.
Knowledge sources
Power in watts is volume times unit demand. The W/m³ figure is a practical assumption, not a full design code. Power and volume units below from NIST and the watt definition.
Page updated October 12, 2026.