Tools
Cooker Hood Extractor Size Calculator: What Extraction Rate (m³/h) Do You Need?
By the Hill & May team
Updated 2026
A range cooker throws out far more steam, heat and frying smells than a slot-in cooker, so the extractor over it has to move enough air to keep up. This tool sizes the hood two ways: the extraction rate in cubic metres per hour, from the size of your kitchen and how hard you cook, and the hood width, from your hob. The figure most people get wrong is the extraction rate, because a good-looking hood that is under-rated will never clear the air properly.
Your kitchen
Measure the whole room, not just the space near the cooker. Air changes are worked out on the full volume.
Your cooking
Usually 90, 100 or 110cm for a range cooker.
Ducting outside is far better at removing steam and heat. Recirculating hoods only filter, so choose one rated at or above the figure below.
The extraction rate comes from a simple, long-standing rule: your extractor should be able to change all the air in the kitchen several times an hour. Ten changes an hour is the usual minimum; keen cooks with a large range cooker are better served by around fifteen. Whatever the room works out at, an extractor sited over the hob must also meet the Building Regulations (Approved Document F) minimum of 30 litres per second, which is 108 m³/h, so this tool never recommends less than that.
