How do I calculate CFM for a room?

CFM (Cubic Feet per Minute) is calculated using the formula: CFM = (Room Volume in ft³ × ACH) / 60. First, multiply the room area (sq ft) by the ceiling height (ft) to get the volume. Then multiply by the recommended air changes per hour for your room type, and divide by 60 to convert hours to minutes.

What is ACH (Air Changes per Hour)?

ACH stands for Air Changes per Hour — the number of times the entire volume of air in a room is replaced with fresh air in one hour. Different room types require different ACH values: bedrooms typically need 5-6 ACH, kitchens need 15 ACH due to cooking fumes, and bathrooms need 8 ACH for moisture control.

How do I convert CFM to m³/s?

Multiply CFM by 0.000471947 to get cubic meters per second (m³/s). For example, 100 CFM equals 0.0472 m³/s. Alternatively, multiply CFM by 0.471947 to get liters per second (L/s).

What CFM do I need for a kitchen?

Kitchens typically require 15 air changes per hour (ACH) due to cooking heat, grease, and odors. For a standard 150 sq ft kitchen with 8 ft ceilings (1,200 ft³ volume), you would need approximately 300 CFM: (1,200 × 15) / 60 = 300 CFM.

What is the difference between CFM and ACH?

CFM (Cubic Feet per Minute) measures the actual volume of airflow, while ACH (Air Changes per Hour) measures how many times the room's air is completely replaced per hour. CFM is the equipment specification you need, while ACH is the ventilation standard that varies by room type.

CFM Calculator | HVAC Calculator Pro

Input Parameters

Unit System

Imperial (ft) Metric (m²)

Room Area (sq ft) *

Room Height (ft)

Room Type

ACH Override (optional)

Override the recommended ACH value for this room type

Results

Airflow Requirements

Required Airflow:

-- CFM

Airflow (SI):

-- m³/s

Airflow (L/s):

-- L/s

Room Details

Room Volume:

-- ft³

Room Area:

-- sq ft

Room Height:

-- ft

Air Changes/Hour:

-- ACH

Room Type:

Tip: CFM = (Volume × ACH) / 60. Select ventilation equipment rated at or above the calculated CFM. Final design should be verified by a qualified HVAC professional.

About This Calculator

This CFM calculator determines the required airflow for ventilation based on ASHRAE standards:

Formula: CFM = (Room Volume in ft³ × ACH) / 60
Room type-specific ACH recommendations from ASHRAE 62.1
Results shown in CFM (imperial), m³/s and L/s (SI) simultaneously
Supports both imperial (sq ft / ft) and metric (m² / m) inputs

Results are for preliminary sizing only. Final ventilation design should be verified by a qualified HVAC engineer.

How this CFM calculator works

This tool calculates the required airflow in CFM (Cubic Feet per Minute) based on room volume and air changes per hour (ACH). The ACH value represents how many times the room's air is completely replaced each hour. Different room types require different ventilation rates — kitchens need more airflow due to cooking, while bedrooms need less.

Understanding CFM and ACH

CFM = Cubic Feet per Minute — the standard unit for airflow in North America
ACH = Air Changes per Hour — how often room air is fully replaced
Formula: CFM = (Volume in ft³ × ACH) / 60
1 CFM ≈ 0.4719 L/s ≈ 0.000472 m³/s

FAQ

What ACH do I need for my room?

It depends on the room type: bedrooms need 5 ACH, living rooms 6 ACH, kitchens 15 ACH, bathrooms 8 ACH, and offices 6 ACH. This calculator automatically selects the right ACH based on your room type selection.

How do I convert CFM to liters per second?

Multiply CFM by 0.471947 to get L/s. For example, 100 CFM = 47.2 L/s. This is the standard metric airflow unit used in most international HVAC specifications.

Can I use this for duct sizing?

Yes, CFM is the starting point for duct sizing. Once you know the required CFM, you can use our duct sizing calculator to determine the proper duct diameter based on air velocity and friction loss limits.

📖 Read the Design Guide

CFM Calculator