HVAC CFM Calculator

CFM stands for cubic feet per minute — it's the volume of air an HVAC system, fan, or duct moves every minute. It's the standard way to measure airflow when sizing equipment, registers, grilles, and ducts.

A common rule of thumb is about 1 CFM per square foot of floor space, which is handy for a quick estimate. However, air-changes sizing (room volume × ACH ÷ 60) is more accurate because it accounts for ceiling height and how the room is used.

Air changes per hour is the number of times the entire volume of air in a room is replaced in one hour. Higher ACH means more ventilation. For example, a kitchen needs a high ACH to clear cooking heat and odors, while a bedroom needs much less.

The standard is about 400 CFM per ton of cooling, with a typical range of 350 to 450 CFM per ton. Drier climates often use closer to 450, while humid climates use closer to 350 to remove more moisture.

Multiply the room's length × width × height to get its volume in cubic feet, multiply by the desired air changes per hour, then divide by 60: CFM = Volume × ACH ÷ 60. This calculator does the math for you once you enter the dimensions and pick a room type.

Kitchens typically use around 15 air changes per hour to clear cooking heat, smoke, and odors quickly. Bathrooms typically use around 8 air changes per hour to remove moisture and prevent mold. This calculator includes presets for both.

Divide the CFM by 400 to estimate the tons of cooling: CFM ÷ 400 ≈ tons. For example, 1,200 CFM is roughly 3 tons. It's an approximation because the exact CFM per ton varies with climate and equipment.

Yes, this CFM calculator is completely free with no signup required. Your inputs are saved locally in your browser so they persist between visits, and nothing is uploaded to a server.