Landscaping & Outdoor
Greenhouse Size Calculator
Estimates greenhouse dimensions and glazing area for a plant count
Updated 13 May 2026 · Live
What this tool does
Estimates greenhouse dimensions and glazing area for a plant count.
Greenhouse Size Calculator — enter your {household_size} and growing focus to get a recommended greenhouse size of {result}, based on typical growing-space guidance per person.
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Formula Used
How the greenhouse size calculator works
Estimates greenhouse dimensions and glazing area for a plant count. 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 landscaping and outdoor wastage
Aggregates settle when compacted — add 5–10% to the loose volume ordered. Turf shrinks roughly 5% on delivery as it dries out. 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 greenhouse size
Permitted Development changes in 2008 restricted impermeable front-garden paving over 5 m². Larger areas need planning permission or an approved SUDS solution.
Building Regulations and compliance
Garden outbuildings under Permitted Development are limited by size, height, and distance from the boundary. Check with your local authority before building. 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 bulk aggregates in 1-tonne bulk bags rather than handballed — the labour saving recovers the small premium several times over. 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 greenhouse 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.
Sources & methodology
Estimates greenhouse dimensions and glazing area for a plant count. Every result is calculated from the values you enter, and all inputs are editable.
Frequently asked questions
Is the recommended greenhouse size accurate enough to order a greenhouse?
Use the recommendation as a starting point only. Actual space needs vary with crop choice, layout (staging, pathways, water butts) and how intensively you plan to grow — check the exact external dimensions against your site and supplier's model before ordering.
How is the recommended greenhouse size chosen?
The calculator estimates a minimum growing area from your household size and growing focus (2 m² per person for salads/herbs, 3 m² for mixed veg and flowers, 5 m² for staples such as potatoes), then matches this to the smallest common UK greenhouse size that covers that area. Increase household size or choose a more space-hungry growing focus if you want more headroom.
Is this tool a substitute for professional advice?
No. This tool is a planning estimator only. For works that affect structure, Building Regulations, Party Wall matters, gas, electrics, or drainage to a sewer, consult a suitably qualified professional before proceeding.
Can I adjust the growing area used per person?
The calculator uses fixed guidance figures (2, 3 or 5 m² per person depending on growing focus) drawn from typical allotment/RHS growing-space guidance. These are starting points — if you grow more intensively or extensively, choose the closest growing focus option or simply increase your household size input to get a larger recommended greenhouse.
Spotted something off?
Calculations or display — let us know.
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