The greenhouse size calculator estimates the minimum floor area for your greenhouse based on what you plan to grow, with a 35% buffer for walkways and working room.
Planning Your Greenhouse
Greenhouse planning starts with what you want to grow and works backwards to size. Most gardeners underestimate their space needs — a 12×14 greenhouse that seems enormous when empty fills up completely with a typical hobby gardener's wishlist of tomatoes, herbs, and propagating trays.
Common standard sizes
Hobby greenhouses are typically sold in standard width increments: 6, 8, 10, 12, 14 feet wide. Length can usually be extended in 4-foot modules. An 8×12 (96 sq ft) is the most popular starter size for serious hobby gardeners. Commercial seedling operations typically need 1,000+ sq ft for meaningful production.
FAQ
How much space does each plant type need?
Small herbs/seedlings: 0.5-1 sq ft. Lettuce/greens: 1-2 sq ft. Tomatoes/peppers: 4-6 sq ft per plant. Cucumbers/melons (trained vertically): 2-4 sq ft. Large tropical plants: 4-8+ sq ft. Add 30-40% for walkways and working room.
What is the ideal greenhouse orientation?
Orient the ridge (long axis) east-west for maximum winter sun exposure — this gives the best north-facing roof surface for solar gain in winter. A south-facing aspect is ideal in northern latitudes. Avoid shade from buildings or trees on the south side.
What size greenhouse should a beginner start with?
An 8×10 or 8×12 foot greenhouse is the most popular starter size — large enough to be meaningful but manageable in cost and maintenance. A 6×8 feels very cramped once you add plants and shelving. Go bigger than you think you need — greenhouses fill up fast.
Is this calculator free?
Yes, completely free with no signup required.