Don’t guess your CFM needs! Use our simple guide to calculate the right airflow (CFM) for your cooktop, kitchen size, and cooking habits.

Introduction

This guide helps you find the right CFM for your range hood. CFM means how much air the hood moves. We show how to calculate CFM for your kitchen. We explain why there are different rules. We also tell how to adjust for cooktop type, where you mount it, duct issues, and how much you cook. Use our step-by-step calculator and examples. This helps you pick a hood that clears smoke and grease. It will not be too loud or waste energy. Our advice uses common industry math and fixes. You can use it right away. Also, you may see our Top 5 Reviews of 2025 guide.

The Calculator

What CFM Means and Why It Matters

• CFM definition. CFM means Cubic Feet per Minute. It tells how much air a range hood moves each minute. It is the key measure for how well it vents.
• Why correct CFM matters. The right CFM takes away smoke, steam, grease, and fumes from cooking. If CFM is too low, smells and grease stay. If too high, it can be loud and might need extra air from outside.
• Two main ways. You can size hoods by: (a) cooktop width (CFM per inch), or (b) gas BTU (CFM per BTU). Calculators and makers use both. When not sure, pick the bigger number.

Simple Rules of Thumb You Can Use Now

• Electric or induction cooktops. Use about 100 CFM for each 10 inches of cooktop width. So, 10 CFM per inch. For a 30-inch cooktop, start with 300 CFM.
• Gas cooktops. Use about 1 CFM for each 100 BTU of all burners. Always check both the width number and the BTU number. Use the bigger one to be safe.
• Room-size method. Some tools use kitchen size times a cooking factor. This is good for open kitchens. But cooktop rules are more important for catching smoke.
• Island vs wall mount. Island hoods need 20% to 30% more CFM than wall hoods. This is because air moves around and no wall helps.

Step-by-Step CFM Calculator (Practical Method)

Use this easy calculator to find your CFM. Follow the steps with your details.

1. Get your info:
   • Cooktop width in inches (W).
   • If gas, total burner BTU (B). If electric or induction, skip B.
   • How it is mounted: wall or island.
   • Duct length and how many sharp bends (optional).
   • How you cook: Light, Normal, or Heavy.
2. Find base CFM:
   • For electric or induction: Base CFM = 10 times W.
   • For gas: Find two numbers – Width CFM = 10 times W, and BTU CFM = B divided by 100. Base CFM is the bigger one.
3. Change for mount type:
   • If island: Multiply Base CFM by 1.2 or 1.3. Use 1.3 to be safe.
4. Add for duct issues:
   • For each 10 feet of duct, add a little. For each sharp bend, add some CFM. Or, add 5% to 15% for short ducts. Add 15% to 30% for long ducts with many bends.
5. Add for how you cook:
   • Light cooking: no change.
   • Normal cooking: add 10% to 20% CFM.
   • Heavy cooking (like lots of frying): add 25% to 50% CFM.
6. Round up to common hood sizes (like 300, 400, 600, 900, 1200 CFM).

Example for a 30-inch electric cooktop on a wall, normal cooking:

• Base CFM = 10 × 30 = 300 CFM.
• Not island, short duct, normal cooking → so about 300 to 360 CFM → pick a 300 to 400 CFM hood.

Example for a 36-inch gas cooktop, 60,000 BTU, island, heavy cooking:

• Width CFM = 10 × 36 = 360 CFM.
• BTU CFM = 60,000 / 100 = 600 CFM.
• Base CFM = bigger of 360 and 600 = 600 CFM.
• Island times 1.3 = 780 CFM.
• Heavy cooking add 30% ≈ 1014 CFM → round to 1000 or 1200 CFM hood.

Detailed Calculation Methods Explained

Width-based method

• Why: The hood needs to cover the cooktop. Wider cooktops have more air to move. Rule: 100 CFM per 10 inches of width. So, 10 CFM per inch.

BTU-based method for gas

• Why: Gas burners make heat and fumes. Sizing by BTU makes sure the hood can remove them. Rule: 1 CFM per 100 BTU. Example: 50,000 BTU means 500 CFM.

Room-volume and activity factors

• Why: Open kitchens or tall ceilings need more power to clear air. Some tools use kitchen size times a cooking factor. This adds to the cooktop CFM.

Why pick the larger CFM

• Catching smoke at the cooktop is key. If BTU CFM is bigger than width CFM, use BTU CFM. It handles heat and fumes better.

Corrections for Ducting and System Losses

• Long ducts and bends lower CFM. Each bend, long duct, or small duct cuts how much air moves. So, add extra CFM when sizing.
• How much to add:
• Short duct with one bend: add 5% to 10%.
• Long duct (over 15 feet) or many bends: add 15% to 30% or more.
• If duct is too small, the fan struggles and moves less air. Use the big duct size the hood manual says.
• Inline blower or hood blower: An inline blower is better for long ducts. It is quieter at the stove. Think about this if your duct is complex.

You ma interested to read: Ducted vs Ductless Range Hoods: Which Is Right for Your Kitchen?

Mount Type Effects and Capture Area

• Wall hoods have a wall behind them. This helps catch smoke better than island hoods.
• Island hoods must catch smoke from all sides. Air currents can blow smoke away. So, add 20% to 30% more CFM for islands.
• Hood width: Make the hood as wide as the cooktop or wider. A wider hood can catch smoke better. But for gas, still use the BTU CFM.

Noise, Sones, and Practical Tradeoffs

• More CFM often means more noise. Makers list sones for noise. Under 3 sones is quiet. 3 to 5 sones is okay. Over 6 sones is loud.
• How to balance power and noise:
• Pick hoods with multiple speeds. Use low for light cooking and high for heavy.
• Use a remote blower. It puts the motor away from the kitchen. This makes it quieter at the stove.
• Choose motors like brushless DC and insulated hoods. They are quieter for the power.
• Tip: If you cook a lot of heavy food, get higher CFM. But spend on a good blower to keep noise down.

Make-up Air and Building Codes

• High CFM hoods (over 400 to 1000 CFM) might need extra air from outside. This replaces the air pulled out. It stops air pressure problems. Check your local rules and ask an HVAC expert.
• If your home is air-tight and you have a strong hood, talk to a pro. They can make sure air flows right or add extra air.

Choosing the Right Motor and Filter Type

• Where to put the motor:
• Internal motor in the hood. This is common and cheap. Good for short ducts.
• Remote motor in the attic or duct. Quieter at the stove. Better for long ducts.
• External motor outside. Very quiet but costs more and is harder to set up.
• Filters:
• Baffle filters are metal. They catch grease well. You can wash them. Best for heavy cooking.
• Mesh filters cost less but need cleaning often.
• Charcoal filters for hoods with no duct. They help with smells but not steam or heat.

Installation Practicalities and Checklist

• Make hood width same as cooktop or wider by 3 to 6 inches per side.
• Put the hood at the height the maker says. Usually 18 to 30 inches above the cooktop.
• Use the duct size the hood needs. Use few bends. Solid duct is better than flexible duct.
• If no duct, make sure you can get charcoal filters and know when to change them.
• Test the hood after putting it in. Run it high. See if it catches smoke and steam well. Check that air flows out outside. Visit here to see full guide.

Maintenance to Preserve Performance

• Clean metal filters every 1 to 2 months. Use hot soapy water or dishwasher. Change charcoal filters every 6 to 12 months for ductless hoods.
• Check ducts each year for grease. Clean if needed.
• Use LED bulbs to cut heat and save energy.
• Listen to the motor. If it gets louder or shakes, the motor might be wearing out. See here for complete guide.

Worked Examples and Quick Reference Table

• 24-inch electric cooktop, light cooking, short duct: Start with 240 CFM. Pick a 250 to 300 CFM hood.
• 30-inch electric cooktop, normal cooking, 10-foot duct, one bend: Base 300 CFM. Add 10% for duct → 330 CFM. Pick a 350 to 400 CFM hood.
• 36-inch gas cooktop, 50,000 BTU, on wall, heavy frying: BTU CFM = 500, Width CFM = 360. Base = 500. Add 30% for heavy cooking → 650 CFM. Pick a 700 to 900 CFM hood.
• 36-inch gas cooktop, 60,000 BTU, on island: Base = 600. Island times 1.3 = 780. Heavy cooking add 25% → about 975 CFM. Pick a 1000 to 1200 CFM hood.

(These examples use the calculator steps and round to common hood sizes.)

Quick Buying Guide and Final Checks

• Always check your CFM number with the hood’s specs. See CFM for your duct setup.
• Choose hoods with many speeds. Good high speed for heavy cooking. Good low speeds for daily use.
• If you hate noise, think about remote blowers or models with low sones at your CFM.
• For gas stoves, use the BTU CFM first. Follow local rules for extra air if needed.
• For tested hoods, see here.

Conclusion

Finding the right CFM is easy. Use the width rule: 10 CFM per inch. For gas, use the BTU rule: 1 CFM per 100 BTU. Then adjust for island, duct issues, and how you cook. Add extra for complex ducts. Pick a hood with multiple speeds or a remote blower to keep noise low. Use our examples and steps to find your CFM. Then buy a hood that meets that CFM with your ducts. With the right size, your kitchen stays clean, fresh, and safe when you cook.