Landscaping & Outdoor
Greenhouse Size Calculator
Estimates greenhouse dimensions and glazing area for a plant count
Updated 26 June 2026 · Live
What this tool does
Estimates greenhouse dimensions and glazing area for a plant count.
Greenhouse Size Calculator — for a household of {household_size} people growing {growing_type}, the estimated minimum growing area and recommended greenhouse size is {result}.
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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 Australian trade formula, and returns a quantity with an indicative cost. Every figure is an estimate — site conditions always move the final number.
Typical Australian 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 Australian 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 National Construction Code (NCC) compliance. Those remain the responsibility of a suitably qualified designer, surveyor, or your building surveyor.
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.
the National Construction Code (NCC) and compliance
Garden outbuildings under Permitted Development are limited by size, height, and distance from the boundary. Check with your local council before building. When in doubt, a pre-application enquiry to the local council 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
Are greenhouse size calculator results accurate enough to order materials?
Use them as a starting estimate only. Verifying the final quantity with your supplier or contractor before ordering is good practice — site conditions, wastage and cut-offs all affect the true figure.
How is the growing area worked out?
The calculator multiplies household size by an area-per-person guide rate: about 2 m² per person for salads and herbs, 3 m² for mixed vegetables and flowers, and 5 m² for space-hungry staples like potatoes. It then suggests the smallest common greenhouse size that meets or exceeds that minimum area.
Does this replace professional advice?
No. This tool is a planning estimator. For works that affect structure, the National Construction Code (NCC), boundary or dividing-fence, gas, electrics, drainage to a sewer, or similar, consult a suitably qualified professional.
Can I change the growing area assumptions?
The area-per-person rates used (2, 3 or 5 m² depending on growing focus) are general allotment/RHS-style guidance, not a fixed rule. If your household grows more intensively or wants extra space for propagation, storage or seating, choose the next size up from the recommendation.
Spotted something off?
Calculations or display — let us know.
Related tools
Calculators from other categories that planners often reach for next.