How big an exhaust fan do I need?

For bathroom fans, range hoods, and room air flow. CFM is cubic feet of air per minute.

Room length (ft)Room width (ft)Ceiling height (ft)Room

Fan size

90 CFM

Air changes per hour8

Room volume640 cu ft

How to measure

Measure the room's length, width, and ceiling height, and pick the room type.

Tips from the field

Bathroom fans should move at least 1 CFM per square foot of floor, and never less than 50 CFM.
Always vent bath fans outside, never into the attic.

What you'll need

Bathroom exhaust fanRange hoodDuct and vent capFan timer switch

Common questions

What size bathroom fan do I need?

At least 1 CFM per square foot of floor, with a minimum of 50 CFM.

Can a bath fan vent into the attic?

No. Always vent outside through the roof or a wall.

What is CFM?

Cubic feet of air per minute that a fan moves.

Add this calculator to your websiteFree

Contractors, bloggers, and real estate agents can put this calculator on their own site for free. Copy the code below and paste it into any page.

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<p style="font:14px sans-serif">Free <a href="https://housecalcs.com/tools/cfm-calculator">room air flow (cfm) calculator</a> from HouseCalcs</p>
<script>window.addEventListener("message",function(e){if(e.origin==="https://housecalcs.com"&&e.data&&e.data.hcSlug==="cfm-calculator"){var f=document.getElementById("hc-cfm-calculator");if(f)f.style.height=e.data.hcHeight+"px"}});</script>

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