Kitchen Extractor / Hood Size Calculator

How the kitchen extractor / hood size calculator works

Recommends extractor fan size and extraction rate for a hob. The calculator takes your dimensions and supplier rates, applies a standard UK trade formula, and returns a quantity with an indicative cost. Every figure is an estimate — site conditions always move the final number.

Typical UK kitchen wastage

Cabinets and worktops are cut to size — wastage is in the offcuts (typically 10% by m²) and any mismeasure that needs re-ordering. Our defaults reflect common UK trade allowances, and can be adjusted upwards for non-standard geometry or downwards where experience supports a lower figure.

What this tool does not do

It does not replace a professional quote, factor regional pricing, assess structural adequacy, or confirm Building Regulations compliance. Those remain the responsibility of a suitably qualified designer, surveyor, or your building control officer.

On-site considerations for kitchen extractor / hood size

Extractor ventilation and electrical circuits must meet Approved Documents F and P. A new cooker hood above 400 m³/h typically needs dedicated ducting, not recirculation.

Building Regulations and compliance

Kitchen electrical work (new circuits, additional sockets beyond a same-circuit extension) is notifiable under Part P. Use a Competent Person Scheme electrician to self-certify. When in doubt, a pre-application enquiry to the local authority can give early clarity, which tends to be less costly than retrospective correction.

Before you order

Order sanitaryware, worktops, and cabinets on the same lead time so site sequence does not stall. Worktops typically sit at 4–6 weeks from template to delivery. Cross-checking the calculator’s output against a supplier quote helps catch differences in pricing assumptions — ask for exact product specifications (grade, finish, batch number) and confirm delivery timescales against your programme.

Adjusting the defaults

Every input in this calculator is editable. Enter your own dimensions, supplier prices, and wastage allowance — the output recalculates instantly. If the defaults feel off for your region or project type, your own numbers always override them.

Using this kitchen extractor / hood size calculator alongside other BuildMetricLab tools

This calculator works best as part of a planning workflow. Pair the quantity with our project contingency, labour-hours, and material-cost calculators to build a complete estimate before you pick up the phone to a supplier. All BuildMetricLab tools run entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the maths.