How to Measure for a Kitchen Hood: Separating Fact from Assumption

What Measuring a Kitchen Hood Actually Means

Measuring for a kitchen hood is not a single number. It involves four distinct dimensions: the hood's width, its depth, its mounting height above the cooking surface, and the airflow capacity measured in cubic feet per minute (CFM). Each serves a different purpose, and confusing them leads to poor performance or an awkward fit.

The scope of the task also depends on your installation type. A ducted hood that vents outside needs clearance for ductwork, while a recirculating hood only requires space for filters and a charcoal insert. An island hood hangs from the ceiling, so its measurements relate to ceiling height and cabinet clearance, not a wall. Knowing which type you have changes what you measure.

The reality is that most manufacturers provide a cutout or mounting template in the box. Your job is not to design the hood but to verify that the space you have matches the hood's specifications. Measure the space first, then shop for a hood that fits those numbers—not the other way around.

• Width: the horizontal span of the hood's underside, usually matching or exceeding the cooktop width.
• Depth: the distance from the wall to the front edge of the hood, critical for capturing rising smoke.
• Height: the vertical gap between the cooktop surface and the hood's bottom edge.
• Airflow (CFM): the volume of air the hood moves, tied to cooking type and duct run length.

Myth: The Hood Width Must Equal the Range Width Exactly

A common assumption is that a hood should be the same width as the cooktop beneath it. While a 30-inch range often pairs with a 30-inch hood, this is a minimum, not a rule. Industry guidance and most manufacturers recommend the hood be at least as wide as the cooktop, and ideally a few inches wider on each side.

The reason is simple: heat, steam, and grease rise and spread outward as they travel upward. A hood that exactly matches the range's width catches only the column of air directly above the burners, missing the outer edges. Widening the hood by 3 to 6 inches improves capture efficiency noticeably, especially with high-output burners.

Reality check: a hood that is wider than the range is rarely a problem visually or functionally, provided it is centered and the surrounding cabinets allow it. The real constraint is space—wall cabinets on either side may limit how wide you can go. Measure the distance between cabinets or walls, then choose the largest hood that fits that gap and meets the minimum width requirement.

Myth: Mounting Height Is a One-Size-Fits-All Number

Many people assume there is a single universal height for hanging a hood. In reality, the recommended clearance depends on the heat source. For gas cooktops, the hood's bottom edge should sit between 24 and 30 inches above the cooking surface. For electric and induction cooktops, the range is tighter, usually 18 to 24 inches.

The difference exists because gas flames produce more heat and combustion byproducts, so the hood needs more distance to avoid heat damage and to allow flames to pull air naturally. Electric and induction surfaces run cooler, so the hood can sit lower and still capture steam and odors effectively.

The reality is that these ranges are guidelines, not laws. Your specific hood model may have a different minimum clearance printed in the manual, often for fire safety. Always check that document first. Also, consider your own height: a hood mounted too low can obstruct your view of the cooktop or bump your head, so factor in the primary cook's height when choosing where in the range to mount it.

Myth: Duct Size and Hood Size Are Independent

Some shoppers focus only on the hood's visible dimensions and ignore the ductwork. That is a mistake. The duct's diameter and length directly affect airflow performance. A hood rated for 600 CFM will not deliver that airflow if the duct is too narrow, too long, or has too many bends.

For ducted hoods, common duct sizes are 6 and 8 inches in diameter, with larger hoods often requiring 8 inches or more. The general rule is that the duct diameter should match the hood's outlet size, and the total duct run should be as short and straight as possible. Each 90-degree bend adds resistance equivalent to several feet of straight duct, reducing effective airflow.

Reality: you cannot measure a hood in isolation. Measure the available space for duct routing—through a wall, up through the ceiling, or into a soffit—and note the distance and number of turns. If the existing duct is smaller than the hood's outlet, you will need an adapter that restricts flow, or you may need to select a hood with a lower CFM rating. This is why measuring the duct path is as important as measuring the hood itself.

Myth: CFM Is the Only Number That Matters for Performance

CFM is the most quoted specification, but it is not the whole story. A hood with high CFM but poor capture area or a poorly matched duct will underperform. The shape of the hood, the depth of its canopy, and whether it has baffle filters or mesh filters all affect how effectively it pulls air.

The common advice is to calculate minimum CFM by multiplying the cooktop's width by 100 for electric stoves, or by 100 per 10,000 BTUs for gas stoves. For example, a 30-inch electric cooktop suggests at least 300 CFM, while a gas range with 40,000 total BTUs suggests 400 CFM. These formulas give a starting point, not a final answer.

Reality: if your kitchen is open to a large room, you may need more airflow to handle the total space. If your duct run is long or has bends, you need a higher CFM rating to compensate. Conversely, an oversized hood with excessive CFM can be noisy and pull conditioned air out of the room. Measure your cooktop, note your duct run, and choose a hood with a CFM rating that matches your actual conditions, not just the maximum number you can find.