The Room Volume Calculator calculates how much air space a room holds, in cubic feet, cubic meters and liters. It handles rectangular rooms, L-shaped rooms and rooms with a sloped ceiling.
Room Volume Calculator
Room volume in cubic feet, cubic metres and litres — for rectangular, L-shaped and sloped-ceiling rooms.
Room volume is length × width × ceiling height for a simple room. It is the number you need for ventilation and air-change rates, air purifiers, dehumidifiers and heating or cooling estimates.
Formula
- Rectangular: V = L × W × H
- L-shaped: V = (L₁ × W₁ + L₂ × W₂) × H
- Sloped ceiling: V = L × W × (h₁ + h₂) ÷ 2
Where h₁ = low wall height and h₂ = highest point. Conversions: 1 ft³ = 0.0283168 m³; 1 m³ = 1,000 L.
How the Calculation Works
Step 1: Find the floor area (split L-shaped rooms into two rectangles).
Step 2: Multiply by the ceiling height — or by the average height for a sloped ceiling.
Step 3: Convert to the unit you need.
Example Calculation
Rectangular room
Given: 15 × 12 ft, 8 ft ceiling
V = 15 × 12 × 8 = 1,440 ft³ ≈ 40.8 m³ ≈ 40,780 L
L-shaped room
Given: 15 × 12 ft plus 8 × 6 ft, 8 ft ceiling
V = (180 + 48) × 8 = 1,824 ft³
Sloped ceiling
Given: 15 × 12 ft, walls 8 ft rising to 12 ft
V = 180 × (8 + 12) ÷ 2 = 1,800 ft³
Dimensions Explained
- The sloped-ceiling average works for a single slope or a symmetric cathedral ceiling rising evenly to a central ridge.
- Built-in cabinets and furniture reduce the actual air volume slightly; volume here is the empty room.
Using Room Volume
Air changes per hour (ACH) = airflow per hour ÷ room volume. For example, a fan moving 100 ft³/min (6,000 ft³/h) in a 1,440 ft³ room gives about 4.2 air changes per hour.
Frequently Asked Questions
How do I calculate the cubic feet of a room?
Multiply length × width × height in feet.
How many cubic feet is a 12 × 12 room?
With an 8 ft ceiling: 12 × 12 × 8 = 1,152 ft³.
How do I convert cubic feet to cubic meters?
Multiply by 0.0283168.
How do I calculate the volume of a room with a vaulted ceiling?
Multiply the floor area by the average of the lowest and highest ceiling heights.
Why is room volume important for HVAC?
Ventilation, air purifier and some heating estimates depend on the volume of air to treat.