What size range hood do you need? Answer in 30 seconds.
Divide the total BTU output of all burners by 100. A 60,000 BTU cooktop needs about 600 CFM. Heavy frying or wok cooking? Size up one step.
Multiply the cooktop width in inches by 10. A 30-inch electric or induction cooktop needs about 300 CFM.
At least as wide as your cooktop — ideally 3 inches wider on each side so it captures everything. A 30-inch cooktop pairs well with a 36-inch hood.
Generally yes for hoods over 400 CFM — most building codes (IRC) require a makeup-air system so your home doesn't go negative pressure. Check local code.
Up to 400 CFM: 6-inch round. 400–750 CFM: 8-inch. 750–1200 CFM: 10-inch. Above that: 12-inch or talk to a pro. Bigger is quieter — never downsize the duct below the hood's outlet.