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MyFloorPlanMaker

Room Volume Calculator

Enter a room’s inside width, length and ceiling height, and the room volume calculator gives the volume of air it holds in cubic meters, cubic feet and litres. It also handles L-shaped rooms, a ceiling that slopes one way, and boxed-in spaces such as a stair cupboard that you want to take out.

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Room volume calculator

Bare numbers are meters; 190 mm works too.

 

 

Enclosed spaces to subtract (boxed-in stair, built-in cupboard)
Floor area
15.12 m²
162.8 sq ft
Room volume
40.824 m³
1,441.7 cu ft
Subtracted
0.000 m³
0.0 cu ft
Net volume
40.824 m³
1,441.7 cu ft
Net volume in litres
40,824 L

This room holds 40.824 m³ (1,441.7 cu ft) of air.

Notes

  • Measured inside the walls, floor to ceiling.
  • Product labels quote room size in different ways (floor area or volume); compare like with like.
  • “Design this room” opens a room whose inside is 4.20 m (13′ 9″) × 3.60 m (11′ 10″); the editor uses its own wall height.
4.20 m3.60 m
How this was calculated
  • Floor area = width × length (L-shape: width × length − cut-out width × cut-out length)
  • Volume = floor area × ceiling height (single slope: × (low + high) ÷ 2)
  • Net volume = volume − Σ (width × length × height × count) of the spaces subtracted
  1. Floor area = 4.20 m × 3.60 m = 15.12 m²
  2. Room volume = 15.12 m² × 2.70 m = 40.824 m³
  3. Net volume = 40.824 m³ − 0.000 m³ = 40.824 m³ = 40,824 L
Design this room

How the volume is worked out

  1. Floor area

    Width times length. For an L-shape, the notch missing from one corner (its width times its length) is taken off.

  2. Times the height

    A flat ceiling multiplies the floor area by the ceiling height. A single-slope ceiling uses the average of the low and high sides.

  3. Less enclosed spaces

    Each boxed-in space you list (width × length × height × how many) is subtracted. If they add up to more than the room, the net volume shows zero and a note asks you to check them.

  4. In three units

    Results show cubic meters and cubic feet side by side, plus litres. One cubic foot is exactly 0.028316846592 m³ and one cubic meter is 1,000 litres.

Worked example in meters and in feet

A room 4.2 m wide and 3.6 m long has 4.2 × 3.6 = 15.12 m² of floor. With a 2.7 m ceiling its volume is 15.12 × 2.7 = 40.824 m³, which is about 1,441.7 cubic feet or 40,824 litres.

In feet, a room 14 by 12 ft has 168 sq ft of floor. With a 9 ft ceiling it holds 168 × 9 = 1,512 cubic feet, about 42.82 m³. Type either set of numbers into the calculator and you get the same figures, with the steps listed under “How this was calculated”.

Sloped and vaulted ceilings

For a ceiling that rises in a straight line from one wall to the opposite wall, measure the height at both walls. The calculator averages them, (low + high) ÷ 2, and multiplies by the floor area. That is exact for a straight single slope across the whole room.

A vaulted ceiling that rises to a ridge in the middle is two slopes. Work out each half as its own room (half the width, the full length, low height at the wall and high height at the ridge) and add the two results. Dormers, curved ceilings and slopes that stop part-way across need splitting the same way.

Measuring ceiling height

Measure from the finished floor to the underside of the ceiling, in two or three places: older floors and ceilings are rarely level. If the readings differ by more than a centimeter or so, use their average for a flat ceiling. Leave out beams, bulkheads and light fittings unless they take up a real share of the room.

Volume or floor area?

Floor area tells you how much floor there is to cover or furnish. Volume tells you how much air there is to heat, cool, dry or clean, so two rooms with the same floor area but different ceiling heights can need different equipment. Heaters, dehumidifiers and air purifiers are labelled in different ways: some by floor area, some by volume, some by an air flow per hour. Compare like with like, and use the figure the product’s maker asks for.

Frequently asked questions

How do I calculate the volume of a room?

Multiply the width, the length and the ceiling height, all in the same unit. Meters give cubic meters; feet give cubic feet. For an L-shaped room, work out the floor area first (the full rectangle less the missing corner) and multiply that by the height.

How many cubic feet is a 12 × 12 room with an 8 ft ceiling?

12 × 12 × 8 = 1,152 cubic feet, which is about 32.62 m³.

How do I work out volume with a sloped ceiling?

If the ceiling slopes in a straight line from one wall to the other, multiply the floor area by the average of the lowest and highest heights. Choose “Single slope” in the calculator and enter both heights. For a pitched ceiling with a ridge, work out each side separately and add them.

Should I subtract furniture from the volume?

No. Furniture takes up little of a room’s air and moves around. Only subtract enclosed built-in spaces, such as a boxed-in stair or a full-height cupboard, and only if the use you have in mind calls for it.

How do I convert cubic meters to cubic feet?

Divide by 0.028316846592, or multiply by about 35.315. For example, 40 m³ is about 1,412.6 cubic feet. The calculator shows both units for every result.

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