Range Hood Size Calculator

Formula Used

This calculator offers three common sizing approaches, then adjusts for capture and duct resistance.

BTU method (gas): Base CFM = Total BTU ÷ 100.
Cooktop width method: Base CFM = 100 × (Cooktop width in feet).
Air-change method: Base CFM = (Kitchen volume × 15) ÷ 60.
Adjusted airflow: Recommended CFM = Base × style × capture × open-layout × duct-loss factor.
Equivalent duct length: EqLen = straight length + (10 × elbows) + 15 (cap).

These are practical rules-of-thumb; always follow the hood manufacturer’s specifications and local codes.

How to Use

Choose a sizing method, or leave it on Auto.
Enter cooktop type, width, and total BTU if available.
Enter kitchen dimensions to support the air-change method.
Select hood style and capture preference based on cooking habits.
Add duct length and elbows to estimate resistance losses.
Press Submit to see airflow and hood width above the form.
Use the download buttons to save your result as CSV or PDF.

Example Data Table

Scenario	Cooktop	Kitchen (L×W×H)	Duct (ft, elbows)	Style	Estimated CFM	Hood width
Daily home cooking	Electric, 30 in	12×10×8	15 ft, 2	Wall canopy	~330–450	36 in
Gas with high output	Gas, 36 in, 75,000 BTU	14×12×9	25 ft, 3	Wall canopy	~850–1100	42 in
Island cooktop	Induction, 36 in	16×14×9	20 ft, 2	Island canopy	~650–900	48 in

Examples are approximate and vary by hood design, filters, and installation details.

Airflow targets for effective capture

Good hood sizing starts with capture, not maximum fan speed. A practical target balances smoke removal, comfort, and noise. This calculator estimates airflow using cooktop output, cooktop width, or kitchen air-change rate. It then adjusts for hood style and layout to reflect how well rising plumes are contained during real cooking.

Understanding the airflow methods

Heat-based sizing is useful when total burner output is known, especially for gas appliances. Width-based sizing provides a baseline when output data is missing. Air-change sizing uses kitchen volume to estimate how quickly air can be replaced during cooking events. Comparing methods helps you avoid under-sizing in large rooms or over-sizing for light duty use.

Ducting and pressure losses

Airflow ratings assume smooth ducting with minimal resistance. Long runs, sharp turns, and restrictive terminations reduce delivered airflow. The calculator converts elbows and caps into an equivalent duct length, then applies a conservative loss factor. Keeping ducts short, straight, and properly sealed improves performance more than increasing fan power alone.

Hood width, overhang, and placement

A hood should be wider than the cooking surface to catch plumes that spread outward. The recommended width adds side overhang, with more overhang for island installations. Mounting height also matters: too high reduces capture, too low interferes with cooking. Always confirm the manufacturer’s height range and clearances for your setup.

Practical selection and compliance notes

Choose a model with multiple speeds so daily cooking stays quiet while high-heat tasks remain controlled. Consider filter type, cleaning access, and make-up air planning when airflow is high. Local requirements may trigger make-up air above certain thresholds. Use these results as a planning baseline, then finalize with product specifications and local guidance. If your garden kitchen is semi-enclosed, treat it like an indoor space and vent outside, not into an attic. Match duct diameter to the hood outlet to prevent turbulence. When possible, use a backdraft damper and avoid flexible duct. Plan service access before finalizing cabinet dimensions today.

FAQs

1) Should the hood be wider than the cooktop?

Yes. Extra width improves capture, especially for front burners. Many setups target at least 3 inches of overhang per side, and island layouts often benefit from even more coverage.

2) What if I do not know total BTU?

Use the cooktop width method or air-change method. You can also estimate by adding burner ratings from the appliance label. The calculator’s Auto mode will fall back to width when output is missing.

3) Why do elbows and long ducts increase required airflow?

They increase resistance, which reduces delivered airflow at the hood. Straighter, smoother ducts usually outperform higher fan ratings connected to restrictive ducting.

4) Does an island hood need more airflow?

Often yes. Without a wall behind it, rising plumes spread and cross-drafts disrupt capture. This calculator applies a higher style factor to reflect that real-world behavior.

5) When should I think about make-up air?

If the recommended airflow is high, many homes need a path for replacement air. Some jurisdictions set thresholds near 600 CFM. Check local requirements and the hood manual before purchasing.

6) How should I choose duct diameter?

Match the hood outlet when possible and avoid reducing diameter. Larger ducts lower velocity and pressure loss, helping the hood deliver closer to its rated performance.