What size greenhouse do I need for tomatoes?

Each tomato plant needs about 0.3 m² of floor space. For 10 tomato plants, you need at least a 6x4ft (1.8x1.2m) greenhouse, though an 8x6ft gives more comfortable working room.

What are the most common greenhouse sizes?

The most popular sizes in the UK are 6x4ft (1.8x1.2m), 8x6ft (2.4x1.8m), and 10x8ft (3x2.4m). The 8x6ft is the most versatile for hobby gardeners.

How much growing space do I lose to paths?

Typically 25-35% of floor area goes to paths and staging. This calculator adds a 30% allowance for paths, access, and staging areas.

Should I buy a bigger greenhouse than I need?

Almost always yes. Most gardeners wish they had gone bigger. Extra space is useful for overwintering, seed starting, and unexpected additions.

What orientation should my greenhouse face?

In the UK, a freestanding greenhouse should ideally run east-west to catch maximum winter sun. Lean-to greenhouses are best on south or west-facing walls.

GardenCalcs

Greenhouse Size Calculator — What Size Greenhouse Do I Need

Work out the ideal greenhouse size for your growing plans.

Number of Plants

Main Use

How We Calculate This

The calculator multiplies the number of plants by the space each type needs: tomatoes 0.3 m², peppers 0.25 m², cucumbers 0.5 m², seedlings 0.05 m², and general plants 0.15 m².

A 30% allowance is added for paths, staging, and working space. The result is fitted to a standard 2.4m width (the most common UK greenhouse width) with length rounded to the nearest 0.5m.

Frequently Asked Questions

Related Calculators

Cold Frame Calculator

Calculate cold frame size and capacity for hardening off plants.

Grow Light Calculator

Work out grow light wattage and coverage for indoor growing.

Seed Starting Calculator

Calculate seed quantities with germination rates and succession sowing.

Propagation Calculator

Work out propagator capacity and timing for cuttings and seeds.

Greenhouse Heating Calculator

Calculate heater wattage needed to maintain greenhouse temperature.

Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.