How to Measure for a Kitchen Hood: A Step-by-Step Guide for Ducted and Ductless Models

Why Accurate Measurements Matter Before You Buy

A kitchen hood that is too narrow or hung at the wrong height will not capture smoke and grease effectively, leaving your kitchen hazy and your cabinets sticky. Measuring correctly before you shop saves you from a return, a costly exchange, or an underperforming appliance. The two main types—ducted (vented outside) and ductless (recirculating through filters)—require slightly different measurements, but the basic dimensions of the hood itself are the same.

The critical numbers are the hood's width, the height above the cooktop, the depth (front-to-back), and the duct size for vented models. You also need to know your cooktop's dimensions and the distance to the nearest cabinet or wall, because these affect both fit and clearance. This guide walks you through a realistic scenario so you can apply the same steps in your own kitchen.

Before you start, gather a tape measure, a step stool, a pencil, and paper. Measure twice, especially the width, because that is the dimension that most often causes mismatches. If your kitchen has a tile backsplash or an uneven wall, measure at several points and use the largest value for clearance calculations.

Step 1: Measure the Cooktop Width and Depth

The hood should be at least as wide as the cooktop, and ideally a few inches wider to capture rising steam and smoke that spread outward. For a standard 30-inch range, a 30-inch hood is the minimum; a 36-inch hood is a better choice if you have the space, because it covers the outer burners more completely. For a cooktop that is 36 inches wide, choose a hood that is 36 inches or larger—never smaller.

Measure the cooktop from left to right across the top, not the base. Write down this number. Then measure the depth from the front edge of the cooktop to the back edge (usually 18 to 22 inches for a standard range). The hood's depth should be at least equal to the cooktop's depth so that the rear burners are covered. Most hoods are 18 to 20 inches deep, which works for standard ranges.

In our scenario, the cooktop is 30 inches wide and 19 inches deep. That means a 30-inch hood will meet the minimum, but a 36-inch hood would provide better coverage. For the purpose of this example, we'll assume you decide to go with a 36-inch hood, which is a common upgrade.

Step 2: Measure the Height Above the Cooktop

The mounting height is the distance from the cooking surface to the bottom of the hood. For gas cooktops, the recommended clearance is typically 24 to 30 inches; for electric, it's 18 to 24 inches. These ranges come from safety and performance—too low and the hood may be a fire hazard or block your view; too high and it won't capture grease effectively. Check your hood's manual for the exact range, as some models have specific requirements.

To measure, place the tape measure vertically from the top of the cooktop to where the bottom of the hood will be. If you already have a hood installed, measure from the cooktop to the underside of that hood. If not, mark the desired height on the wall with a pencil. For a gas range, a common choice is 27 inches; for electric, 21 inches. In our scenario, we'll use a gas range and set the height at 27 inches.

Important: The clearance is measured to the bottom of the hood, not the top. If you have a cabinet above the hood, ensure the top of the hood fits below the cabinet's bottom edge. Also, consider the height of the tallest person who cooks—if the hood hangs too low, it could be a head hazard.

Step 3: Measure the Width of the Installation Space

The hood's width must fit between the cabinets or walls that flank it. Measure the distance between the inside edges of the cabinets to the left and right of the cooktop. If there is a wall on one side, measure from the wall to the inside edge of the cabinet on the other side. Write down this dimension.

The hood itself will have a specified width (e.g., 36 inches), but the actual mounting bracket may require a bit of clearance on each side. Check the manufacturer's spec sheet for the exact mounting dimensions. In general, you need at least 1/2 inch of clearance on each side for the bracket, but some models need more. If the space between cabinets is exactly 36 inches, a 36-inch hood might be too tight—measure the bracket width first.

In our scenario, the space between the cabinets is 37 inches. That gives a 1/2-inch gap on each side for a 36-inch hood, which is enough for most brackets. If the space were only 35 inches, you would need to choose a 30-inch hood instead. Always measure the actual opening, not the cooktop width, because the cabinets define the physical limits.

Step 4: Measure the Duct Path for Ducted Hoods

For a ducted hood, you need to measure the path from the hood's top to the exterior wall or roof. This includes the vertical rise to the ceiling or soffit, any horizontal run to an exterior wall, and the size of the duct that will fit. Most ducted hoods use round ducting, typically 6 or 8 inches in diameter, or rectangular ducting. The hood's outlet size is specified in the manual; match the duct size to that outlet to avoid restricting airflow.

Measure the vertical distance from the top of the hood (at the mounting height) to the ceiling. Then measure the horizontal distance from the hood's center to the nearest exterior wall. If the duct will run through a soffit or cabinet, measure the interior height and width of that space to ensure the duct fits. Add 10% to the total duct length to account for elbows and fittings, which add resistance.

In our scenario, the ceiling is 8 feet (96 inches) high. The hood's top at 27 inches above the cooktop means the hood's top is at 96 - 27 - (hood height, say 10 inches) = 59 inches from the ceiling. The horizontal run to the exterior wall is 24 inches. You would need a duct that goes up 59 inches, then turns 90 degrees and runs 24 inches to the wall. A 6-inch round duct is common for a 36-inch hood rated at 400 CFM. If the run is longer than 10 feet, consider upgrading to 8-inch ducting to reduce noise and maintain airflow.

Step 5: Measure for Ductless Hoods and Recirculating Kits

Ductless hoods recirculate air through charcoal filters and release it back into the kitchen. They don't need ducting, but they do require clearance above the hood for the filtered air to exit. Measure the space between the top of the hood and the cabinet above—most ductless hoods have top vents that need at least a few inches of clearance. Also, check the filter access: you need to be able to reach the filters for replacement, so ensure there's enough space to open the filter hatch.

If you're converting a ducted hood to ductless (some models allow this), you'll need a recirculating kit that includes a charcoal filter and a deflector. The deflector changes the air path from upward to sideways, so you need to measure the clearance to the front of the hood. In our scenario, the cabinet above the hood is 18 inches deep, and the hood is 20 inches deep. That leaves 2 inches of overhang, which is fine for a top-vented ductless hood. For a deflector kit, check the manual for the minimum clearance to the front edge.

Ductless hoods are easier to install because they don't require wall or roof penetrations, but they are less effective at removing moisture and odors. They are best for kitchens where ducting isn't practical, such as apartments. Measure the same width and height as for a ducted hood, but skip the duct path measurements.

Step 6: Calculate the CFM You Need

The hood's airflow rating, measured in cubic feet per minute (CFM), should match your cooking habits and the size of your kitchen. A common rule is to use 100 CFM per 10,000 BTU of gas burner output, or 100 CFM per 36 inches of electric cooktop width. For a gas cooktop with 40,000 BTU total, you need at least 400 CFM. For an electric cooktop, a 30-inch wide cooktop typically needs around 300 CFM.

Another method is to calculate the kitchen volume (length × width × height) and divide by 15 to get the minimum CFM for good air exchange. For example, a 10×10×8 kitchen is 800 cubic feet; 800 ÷ 15 = 53 CFM, which is much lower than the burner-based method. The burner method is more accurate for actual cooking. Use the higher of the two numbers.

In our scenario, the gas cooktop has a total of 40,000 BTU, so you need at least 400 CFM. A 36-inch hood with 400 CFM is a common pairing. If you do a lot of high-heat cooking, consider 600 CFM, but note that higher CFM may require a makeup air damper in tightly sealed homes—check local codes. For ductless hoods, the CFM is often lower because the charcoal filter restricts airflow, so you may need a slightly higher rating.