A range hood is sized to two things: the cooktop it sits over and the cooking that happens under it. The cooktop sets the width. The cooking sets how much air the hood must move and how it should be placed so that steam and grease are captured rather than spread into the room.
Start with the cooking. Describe the household in plain terms. Does it sear meat, fry often, or boil large pots most evenings? A household that cooks lightly can use a modest hood. A household that cooks heavily, or uses a wok or a grill pan, needs a hood with more rated airflow and a capture area that reaches the front burners. If the kitchen is open to a living area, the noise rating matters as much as the airflow, because a loud hood gets switched off.
Measure the cooktop. A hood at least as wide as the cooktop captures more of the rising steam, and that is the usual choice over gas. Compare the hood's listed width and depth with the cooktop's. A hood narrower than the cooktop leaves the outer burners uncovered.
Measure the mounting height. Manufacturers list a range of heights above the cooking surface for each hood. Take the distance from the cooktop surface to the bottom of the hood, and compare it with the ceiling and the cabinet bottom. A hood mounted too high loses capture. A hood mounted too low can be a burn risk and may block a cabinet you use every day. Use the range on the installation sheet, not your estimate.
Settle the ventilation path before you buy. A hood that vents outdoors needs a clear route to an exterior wall or roof, and the route should be short and as straight as the house allows. A recirculating hood needs filters that the household will actually replace. The path changes the install, so the choice belongs in the plan from the start.
Look at the controls and the lighting. Choose controls the cook can reach without looking. Check that the light falls on the cooking surface without casting shadow over the pans. A hood that is hard to switch on gets switched on less, and then it does not capture the cooking it was bought for.
Compare the finished plan with the typical service life figures in the appliance service life ranking, and note the filter and fan in your records. A hood that fits the cooktop, the ceiling, and the cooking is the one that gets used, and a hood that gets used is the one that keeps working as planned.