What does the Greenhouse Size Calculator do?

Calculate greenhouse growing capacity. See how many plants fit by type with common size presets. All calculations are performed in your browser using official UK rates and thresholds.

Does this include delivery costs?

This calculator estimates material quantities and approximate costs. Delivery charges vary by supplier, quantity and location. Bulk orders often qualify for free or reduced delivery.

When is the best time for this project?

Timing depends on the specific project. Generally, spring and autumn are ideal for lawn and planting work, while hard landscaping can be done year-round in dry conditions.

Greenhouse Size Calculator

Calculate greenhouse growing capacity. See how many plants fit by type with common size presets.

Last updated: April 2026 · Source: RHS - Greenhouse Growing Guide

Length (m)

Width (m)

Floor Area

6.0 m²

Usable Growing

4.2 m²

Volume

13.2 m³

How many plants will fit?

Tomato Plants

Cucumber Plants

Pepper Plants

Aubergine Plants

Lettuce

Herb Pots

104

Seed Trays

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

Greenhouse growing area is calculated as the internal floor space in square feet or square metres, minus any permanent staging, pathways, and structural obstructions. A standard 6ft x 8ft greenhouse provides 48 sq ft of total floor area but approximately 36-40 sq ft of usable growing space after accounting for a central path. The calculator converts your chosen dimensions into both usable ground beds and shelved growing capacity.

Plant capacity depends on species spacing requirements at maturity. Tomato cordons need roughly 3 sq ft per plant (18-inch spacing in rows 24 inches apart). Seedling trays (standard UK seed tray is 14" x 9") hold 24-40 plugs and require about 0.9 sq ft of bench space each. Pepper and aubergine plants need 2.5 sq ft each, while cucumber plants require 4 sq ft for adequate air circulation.

Staging and shelving effectively double your growing area for smaller plants and propagation. A 6ft x 8ft greenhouse with staging along both long walls gains an additional 20-24 sq ft of shelf space. The calculator factors in whether you plan ground-level beds for tall crops (tomatoes, cucumbers) or multi-tier staging for compact plants (herbs, lettuce, seed trays), providing a combined plant count estimate.

Planning capacity for a 8ft x 10ft greenhouse

Total floor area: 8 x 10 = 80 sq ft, minus 2ft central path = approx 64 sq ft usable ground
Ground bed allocation: 6 cordon tomato plants (18 sq ft) + 4 cucumber plants (16 sq ft) = 34 sq ft
Remaining ground space: 30 sq ft for aubergines (4 plants) and peppers (6 plants)
Staging along one 10ft wall (2ft deep): 20 sq ft shelf space for 22 seed trays or 40 herb pots
Total growing capacity: 14 large plants at ground level plus propagation space for 500+ seedlings on staging

Source: RHS - Greenhouse Growing Guide

Frequently Asked Questions

What does the Greenhouse Size Calculator do?: Calculate greenhouse growing capacity. See how many plants fit by type with common size presets. All calculations are performed in your browser using official UK rates and thresholds.
Does this include delivery costs?: This calculator estimates material quantities and approximate costs. Delivery charges vary by supplier, quantity and location. Bulk orders often qualify for free or reduced delivery.
When is the best time for this project?: Timing depends on the specific project. Generally, spring and autumn are ideal for lawn and planting work, while hard landscaping can be done year-round in dry conditions.