Match the hood width to your cooktop, then check your kitchen's air volume

The range hood should be as wide as your cooktop or slightly wider. A 30-inch cooktop needs a 30-inch hood minimum; a 36-inch cooktop needs 36 inches. If your cooktop is an odd size, round up rather than down — a hood that overhangs slightly works better than one that falls short of the edges.

Beyond width, you need to know your kitchen's cubic footage and how much air the hood must move per minute. A hood that is the right width but too weak will not clear smoke and steam. A hood that is too powerful for the space can create negative air pressure and pull exhaust back into the house. The balance matters as much as the size.

Most kitchens fall into one of three categories: small and open, medium with some walls, or large with heavy cooking. Your situation determines what power level you actually need, not just what the manufacturer claims.

Key Takeaways

  • The hood width should match your cooktop width or be 1 to 2 inches wider on each side.
  • Cubic feet per minute (CFM) is the measure of how much air the hood moves; most residential kitchens need between 300 and 600 CFM.
  • A kitchen with an open floor plan needs less CFM than a closed kitchen because air can escape more easily.
  • Ducted hoods (vented outside) are more effective than ductless hoods (recirculating), so a ductless hood may need higher CFM to perform the same job.

How to measure your cooktop and choose hood width

Measure the width of your cooktop from the outside edge of one side to the outside edge of the other. Write down the exact number. Standard cooktop widths are 30, 36, 42, 48, and 60 inches, but yours may fall between standard sizes.

Buy a hood that matches that width or is 1 to 2 inches wider. A 30-inch hood over a 30-inch cooktop is acceptable. A 36-inch hood over a 30-inch cooktop is also fine — the overhang helps catch steam that rises at an angle. A 30-inch hood over a 36-inch cooktop is not adequate; smoke and steam will escape at the sides.

If your cooktop is 42 inches or wider, you may need a custom hood or two separate hoods. Many manufacturers do not make hoods wider than 48 inches for standard installation. Check what is available in your area before you measure, so you know what sizes you can actually buy.

Understanding CFM and what your kitchen actually needs

CFM (cubic feet per minute) is the volume of air the hood pulls out of the kitchen per minute. The higher the CFM, the more air it moves. A weak hood will not clear smoke; an oversized hood can create drafts and pull conditioned air out of the house.

A basic rule is 100 CFM per linear foot of cooktop. A 30-inch (2.5-foot) cooktop would need 250 CFM; a 36-inch (3-foot) cooktop would need 300 CFM. However, this rule assumes a moderately enclosed kitchen. Your actual need depends on whether your kitchen is open to the rest of the house.

In an open floor plan where the kitchen flows into the dining room or living room, air can escape easily, so you can use the lower end of the range — often 300 to 400 CFM is enough. In a closed kitchen with a door, you need more power because the air has nowhere to go except up the hood. Closed kitchens often need 400 to 600 CFM. If you cook with high heat or fry frequently, add 100 CFM to your estimate.

Ducted versus ductless: why the type matters for sizing

A ducted hood vents air directly outside through a duct in your wall or ceiling. A ductless hood (also called recirculating) filters the air and pushes it back into the kitchen. Ducted hoods are more effective because they remove heat and moisture entirely. Ductless hoods recirculate some heat and moisture, so they feel less powerful even at the same CFM.

If you are installing a ductless hood, choose one with a CFM rating 20 to 30 percent higher than you would for a ducted hood in the same kitchen. A kitchen that would need 400 CFM ducted might need 500 CFM ductless to feel equally effective.

Ducting also affects performance. A long duct run (more than 10 feet) or a duct with many bends loses efficiency. If your duct run is long or complex, you may need a hood with higher CFM to compensate for the loss. Ask the installer or check the manufacturer's documentation for CFM loss over distance.

Island and wall-mounted hoods have different sizing rules

An island hood hangs from the ceiling above a cooktop in the middle of the room. It must pull air from all sides, so it needs more CFM than a wall-mounted hood over the same cooktop. Island hoods typically need 25 to 50 percent more power than wall hoods.

A wall-mounted hood sits against the wall above the cooktop. Air naturally rises and moves toward the wall, so the hood catches it more easily. Wall hoods are more efficient and need less CFM to do the same job.

If you have an island cooktop, do not use the standard 100 CFM per linear foot rule. Instead, multiply by 1.25 to 1.5. A 36-inch island cooktop would need 375 to 450 CFM instead of 300 CFM.

What happens if you choose the wrong size

A hood that is too narrow will not catch all the smoke and steam. You will notice steam escaping at the sides and smoke lingering in the kitchen. The problem gets worse if you cook with high heat or use the back burners. Undersizing is the most common mistake, and it is frustrating because you cannot fix it without replacing the hood.

A hood that is too weak (low CFM) will not move air fast enough to clear the kitchen. You may hear the fan running at full speed but still smell cooking odors hours later. Weak hoods are often ductless models in closed kitchens, or ducted models with long duct runs and no compensation for the loss.

A hood that is too powerful can create negative air pressure, which pulls exhaust from gas appliances back into the kitchen instead of up the chimney. This is rare in residential kitchens but possible if you install a commercial-grade hood in a small, sealed space. Most residential kitchens will not have this problem, but it is worth knowing if you are considering an unusually large hood.

Checking manufacturer specs and installation requirements

Before you buy, read the hood's specifications sheet. It will list the CFM at the highest fan speed. Some hoods have multiple speeds; the CFM rating is usually for the highest setting. Check whether the CFM is measured with the duct installed or without — the number can be different.

Also check the noise level, measured in sones or decibels. A hood that moves a lot of air but is very loud may not be pleasant to use. Most residential hoods range from 3 to 8 sones; quieter models are available but often cost more.

Look at the installation requirements. Some hoods need a certain amount of clearance above the cooktop (usually 24 to 30 inches). Some require a specific duct diameter (usually 6 or 8 inches). Some need a dedicated electrical outlet. Confirm that your kitchen can accommodate these requirements before you order.

Frequently Asked Questions

Can I use a smaller hood if my kitchen is very open?

Yes, but not smaller than the cooktop width. An open kitchen may need only 300 CFM where a closed kitchen would need 500, but the hood still must be as wide as the cooktop to catch steam and smoke at the edges. Width and power are separate decisions.

What size hood do I need for a gas cooktop versus electric?

Gas cooktops produce more heat and moisture than electric, so they benefit from slightly higher CFM. If you have a gas cooktop, add 50 to 100 CFM to your estimate. The width requirement is the same regardless of fuel type.

Do I need a bigger hood if I cook a lot?

If you cook frequently or use high heat regularly, add 100 CFM to your base estimate. A home cook who uses the cooktop daily and often fries or sears should lean toward the higher end of the range for their kitchen type.

Can I install a hood that is wider than my cooktop?

Yes. A hood that is 2 to 4 inches wider than the cooktop on each side is fine and often preferred because it catches more steam. A hood that is much wider (8+ inches on each side) may look out of proportion and is unnecessary.

What if I cannot fit a ducted hood — is ductless good enough?

Ductless hoods work but are less effective because they recirculate air instead of removing it. If ducting is not possible, choose a ductless hood with CFM 20 to 30 percent higher than you would use for a ducted hood, and expect it to feel less powerful even at maximum speed.