Room Volume Calculator
Type three dimensions. Read volume in any unit, plus HVAC sizing and air-change rates.
How to use
Enter the room dimensions. The calculator returns the volume in four units and shows HVAC sizing and ventilation reference values.
- Enter length, width, and height in your preferred unit (feet or metres).
- Volume appears in cubic feet, cubic metres, US gallons, and litres simultaneously.
- Use the HVAC sizing readout as a rough cooling-load reference (BTU/h). For accurate load calculation, use Manual J or a qualified HVAC contractor.
- The air-changes-per-hour table maps room types to required ventilation rates per ASHRAE 62.2 / Canadian NBC 9.32.
Reviewed 6 June 2026 · methodology cited
About this calculator
Room volume is the cubic space enclosed by the floor, ceiling, and walls. It is the starting point for several building-science calculations: HVAC sizing (how many BTU/h of cooling or heating a room needs), ventilation (how many air changes per hour the room requires to stay healthy), insulation (cubic feet of loose-fill insulation in a cathedral ceiling), and material quantities for finishes that fill a volume rather than cover a surface.
This calculator takes length × width × height and returns the same volume in four units: cubic feet (the North American HVAC standard), cubic metres (the SI / Canadian engineering standard), US liquid gallons (sometimes used for fuel-oil or LP-gas room volume in propane safety codes), and litres (the metric equivalent). It also returns a rough HVAC cooling-load estimate and a reference table of ventilation rates by room type.
The math behind it
Volume = length × width × height. The math itself is trivial; the value of the calculator is in handling unit conversion and providing context.
The unit conversions: 1 ft³ = 0.02832 m³ = 7.481 US gallons = 28.32 litres. So a 12 ft × 14 ft × 9 ft room is 1,512 ft³ = 42.81 m³ = 11,312 gallons = 42,816 litres.
The HVAC cooling-load reference is intentionally rough: about 20 BTU/h per square foot of floor area for an 8-foot ceiling in a normally-sun-exposed residential room (Manual J would refine this with insulation values, glazing area, occupancy, and orientation). For an 8-foot-ceiling room, 20 BTU/ft² ÷ 8 ft = 2.5 BTU/ft³. The calculator multiplies room volume by 2.5 BTU/ft³ to give a sizing reference only — never as a substitute for an actual Manual J load calculation.
Air changes per hour by room type
| Room | Air changes per hour | Source |
|---|---|---|
| Bedroom | 0.35 (continuous) | ASHRAE 62.2 / NBC 9.32 |
| Living room | 0.35 (continuous) | ASHRAE 62.2 |
| Kitchen | 100 cfm at range | ASHRAE 62.2 |
| Bathroom | 50 cfm intermittent | ASHRAE 62.2 |
| Laundry room | 50 cfm intermittent | ASHRAE 62.2 |
| Garage | 100 cfm continuous | IRC, fire/CO safety |
| Mechanical room | 2–4 ACH | NFPA 31 (oil heat) |
| Workshop | 4–6 ACH | OSHA general dilution |
| Office | 0.35 (continuous) | ASHRAE 62.1 commercial |
| Classroom | 0.35 + 10 cfm/person | ASHRAE 62.1 |
HVAC sizing and ventilation
For HVAC sizing the calculator gives only an order-of-magnitude estimate. Real cooling-load calculations (Manual J in the US, CSA F280 in Canada) account for insulation R-values, glazing U-values, solar exposure, occupancy, equipment heat gain, infiltration, and climate zone. A 1,500 ft³ master bedroom in Phoenix needs very different cooling capacity than the same room in Vancouver. Always treat any per-square-foot or per-cubic-foot rule as a check, never as a sizing input.
For ventilation, the rates in the reference table come from ASHRAE 62.2 (US residential) and the Canadian NBC 9.32. Bedrooms need about 0.35 ACH continuous (with bathroom and kitchen exhaust handling peak loads). Bathrooms need 50 cfm intermittent or 20 cfm continuous. Kitchens need 100 cfm intermittent over the range. Garages and high-moisture rooms need significantly higher rates. The calculator converts room volume to required CFM at any chosen ACH rate, which is useful for sizing exhaust fans and supply registers.
Frequently asked questions
How do I calculate the volume of a room?
Multiply the room's length by its width by its ceiling height, with all three dimensions in the same unit. A 12 ft × 14 ft × 9 ft room has a volume of 12 × 14 × 9 = 1,512 cubic feet. For metric, a 3.7 m × 4.3 m × 2.7 m room has a volume of 3.7 × 4.3 × 2.7 ≈ 43 cubic metres.
How many cubic feet are in a cubic metre?
One cubic metre equals 35.3147 cubic feet. The reverse: 1 cubic foot equals 0.0283 cubic metres. The factor comes from (1 m ÷ 0.3048 m/ft)³ = (3.2808 ft)³ = 35.3147 ft³.
Can I use this for HVAC sizing?
Only as a rough reference. The HVAC reading is a per-cubic-foot estimate that does not account for insulation, window area, sun exposure, occupancy, or climate zone — all of which can change the actual cooling load by 30–50 percent. For real HVAC sizing use Manual J (US) or CSA F280 (Canada), performed by a qualified HVAC contractor or mechanical engineer.
What are air changes per hour?
Air changes per hour (ACH) is the number of times the entire volume of room air is replaced with outside air in one hour. A 1,500 cubic-foot bedroom at 0.35 ACH receives 1,500 × 0.35 = 525 cubic feet per hour, which is 525 ÷ 60 = 8.75 cubic feet per minute (cfm) of fresh air. ASHRAE 62.2 sets minimum continuous ventilation rates for dwellings; the table on this page shows common values by room type.
How do I calculate volume for a room with sloped ceilings?
Split the room into two volumes: the lower rectangular part (floor area × wall height) plus the upper triangular wedge (floor area × extra height ÷ 2). For a 12 × 14 room with walls at 8 feet rising to a 12-foot ridge, the calculation is 12 × 14 × 8 + 12 × 14 × (12-8) ÷ 2 = 1,344 + 336 = 1,680 cubic feet. This calculator handles rectangular rooms only; for sloped ceilings, calculate each volume separately and add.
Is this calculator a structural or engineering tool?
No. It is a geometric reference. Structural design — beams, columns, floor systems, foundations — requires a sealed engineering drawing reviewed by a qualified structural engineer working from the local building code. The ventilation and HVAC values shown are likewise references; the actual mechanical design belongs to a mechanical engineer or licensed HVAC contractor.