Volume Calculator

Calculate room or space volume in cubic feet, cubic meters, gallons, and liters

Knowing the volume of a room is essential for a range of practical applications, from sizing HVAC equipment to estimating paint coverage. Volume tells you the total three-dimensional space inside a room, measured in cubic units. For a standard rectangular room, the formula is simple: length times width times height.

For example, a room that is 20 feet long, 15 feet wide, and 8 feet tall has a volume of 2,400 cubic feet. If the space is cylindrical, such as a silo, tank, or rounded turret, you use the formula pi times the radius squared times the height.

HVAC professionals use room volume to determine the correct size of heating and cooling systems. An undersized unit will struggle to maintain comfortable temperatures, while an oversized unit cycles on and off too frequently, wasting energy and causing uneven temperatures. The general rule of thumb is that you need about 1 BTU per cubic foot per degree of temperature change.

Air exchange rates also depend on volume. Ventilation standards often specify a number of air changes per hour (ACH). For a bedroom, the recommendation is typically 4 to 6 ACH, which means the entire volume of air in the room is replaced 4 to 6 times every hour. Knowing your room volume lets you calculate the required airflow in cubic feet per minute (CFM).

Building codes often reference room volume when setting minimum requirements for habitable spaces. For instance, many jurisdictions require a minimum ceiling height of 7 feet and a minimum room area of 70 square feet for a bedroom, which translates to a minimum volume of 490 cubic feet.

Indoor air quality assessments also rely on volume calculations. When measuring pollutant concentrations, the volume of the space determines how quickly contaminants dilute. Larger volumes provide more dilution, which is why open floor plans tend to have better air quality than small enclosed rooms with the same ventilation rate.

This calculator provides results in four common units. One cubic foot equals approximately 0.0283 cubic meters, 7.48 gallons, and 28.32 liters. The gallon and liter conversions are especially useful when calculating water capacity for tanks, pools, or plumbing systems. For international projects, cubic meters are the standard unit used in most countries outside the United States.