How this calculator works
There are two standard ways to size a range hood. The first goes by the cooktop: for gas, one cubic foot a minute (CFM) for every 100 BTU of burner output, and for electric or induction, 100 CFM for every 10 inches of cooktop width. The second goes by the kitchen: enough to change the air about 15 times an hour, which is the room volume times 15 divided by 60. Use the higher of the two, and add about 25% for a hood over an island, which has no wall to help it capture the fumes.
Worked example: a gas cooktop with 60,000 BTU of burners needs 600 CFM. A 14 × 12 × 8 ft kitchen (1,344 ft³) needs 336 CFM for 15 air changes an hour. The higher figure, 600 CFM, is the one to shop for, with an 8 inch duct. Over an island it would be 750 CFM.
CFM by gas range output (wall-mounted hood)
One CFM per 100 BTU, checked against a 14 × 12 × 8 ft kitchen.
| Total burner output | Wall hood | Island hood | Duct size |
|---|---|---|---|
| 30,000 BTU | 350 CFM | 450 CFM | 6 in |
| 40,000 BTU | 400 CFM | 500 CFM | 6 in |
| 50,000 BTU | 500 CFM | 650 CFM | 8 in |
| 60,000 BTU | 600 CFM | 750 CFM | 8 in |
| 80,000 BTU | 800 CFM | 1,000 CFM | 10 in |
| 100,000 BTU | 1,000 CFM | 1,250 CFM | 10 in |
Tips before you buy
- Vent it outside. A recirculating hood only filters grease and does little for moisture, heat and combustion gases. Gas cooking especially needs outdoor venting.
- A hood should be as wide as the cooktop or wider, and mounted 24 to 30 inches above it (follow the maker's instructions). A narrower or higher hood captures less.
- Use the smoothest, shortest, straightest duct you can with smooth rigid metal pipe. Each elbow cuts the airflow, and flexible ducts are worse.
- Look at the noise rating (sones) and the speed settings. A quiet low speed you will actually use is better than a loud 900 CFM fan you avoid.
- Hoods over 400 CFM may need make-up air so that the fan does not pull exhaust gases back down other flues. Your local code decides.
Tools & materials for this project
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Frequently asked questions
How many CFM do I need for a gas range?
About 1 CFM for every 100 BTU of burner output. A typical 60,000 BTU range needs about 600 CFM, and a 36 inch pro-style range of 100,000 BTU needs 1,000 CFM.
What size range hood do I need for a 30 inch electric range?
About 300 CFM by the cooktop rule (100 CFM per 10 inches of width), though most people choose 300 to 400 CFM. The hood should be at least as wide as the cooktop.
Do I need make-up air for a range hood?
Many codes require it above about 400 CFM, because a strong hood can pull exhaust gases back down other flues. Check with your building department.
Do range hoods over an island need more CFM?
Yes, about 25 to 50% more, because there is no wall behind the cooktop to help capture the rising fumes, and cross-drafts pull it away.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.