Greenhouse Size Calculator
Pick the right greenhouse footprint from plant counts and aisle preference. Outputs total square footage, m², and recommended dimensions for a hoop house, glass greenhouse, or lean-to.
Sizing the soil to fill it? Pair with the Raised Bed Soil Calculator, the Container Garden Soil Calculator, and the Compost Calculator.
Estimate your greenhouse size
Enter how many plants of each type you want to grow, then pick aisle width.
10 ft x 12 ft hoop house
42 plants total, 87 sq ft of plant area at standard aisle = 130 sq ft (12.1 m²) recommended.
How to use this calculator
Enter how many plants you want to grow in each category. Trellised vining (the default) cuts the cucumber and squash footprint significantly compared to sprawling them on the ground. Pick aisle width based on whether you need wheelbarrow access (wide), normal walking (standard), or just enough for one person to step sideways (narrow). The result is the smallest greenhouse that fits all your plants plus aisle space.
Tips for accurate sizing
- Be honest about full-grown size. A tomato seedling needs 4 sq ft, but at full height with cages and air circulation, plan for the full 5 sq ft. The calculator uses full-grown values; sizing for seedlings shrinks the result by 60 to 70 percent.
- Trellis vining plants whenever possible. A trellised cucumber takes 2 sq ft; the same plant sprawled takes 7. For greenhouses, vertical growing is almost always the right choice.
- Add 10 to 20 sq ft for support gear. Potting bench, water barrel, fan, heater, supply storage. The calculator covers plants and aisles only.
- Greenhouse rectangles work better than squares. A 10 x 14 (140 sq ft) layout fits a center aisle with two rows of beds; a 12 x 12 of the same area is awkward to lay out. Pick longer-than-wide.
- Standard aisle is 24 to 30 inches. Below 24, harvesting awkward; below 18, you cannot kneel to weed. Wheelbarrows or carts need 36+.
Hoop house vs glass greenhouse vs lean-to
| Type | Cost / sq ft | Life | Best for |
|---|---|---|---|
| Hoop house (PVC + poly film) | $1 to $3 | 3 to 5 yr per film | First greenhouse, scale-up, seasonal use, large footprint on a budget. |
| Hoop house (galvanized steel + poly) | $3 to $6 | 10 to 15 yr | Permanent installation in windy or snowy regions; commercial-grade. |
| Polycarbonate panel | $8 to $15 | 10 to 20 yr | Year-round use; better insulation than poly film; mid-budget permanent. |
| Glass greenhouse | $25 to $50 | 20+ yr | Permanent feature, aesthetic priority, climate-controlled use. |
| Lean-to (any material) | 50 to 70% of standalone | Same as material | Limited yard, south-facing wall, shared utilities with house. |
Recommended footprints by total area
- Under 60 sq ft (5.6 m²): 6 ft x 8 ft lean-to. Suits 30 to 50 leafy greens or a herb-and-seedling tray.
- 60 to 100 sq ft (5.6 to 9.3 m²): 8 ft x 10 ft lean-to or 10 ft x 10 ft hoop. Adds 4 to 6 fruiting plants on top of leafy and herb capacity.
- 100 to 150 sq ft (9.3 to 13.9 m²): 10 ft x 12 ft hoop or 8 ft x 16 ft lean-to. The classic 'family-of-four' size; covers a full vegetable mix.
- 150 to 250 sq ft (13.9 to 23.2 m²): 10 ft x 16 ft, 10 ft x 20 ft, or 12 ft x 16 ft hoop. Suits 8 to 12 fruiting plants plus full leafy and herb capacity.
- 250 to 400 sq ft (23.2 to 37.2 m²): 12 ft x 20 ft to 14 ft x 24 ft hoop. Approaching small-market gardener territory; consider commercial-grade hardware.
- 400+ sq ft (37.2+ m²): 14 ft x 32 ft+ hoop or multiple smaller greenhouses. Verify local zoning before building; many jurisdictions permit different rules above 400 sq ft.
Common mistakes
- Sizing for seedlings, not mature plants. Tomato plants are tiny in May and 5 ft tall in August. Always calculate from full-grown size.
- Skipping aisle space. A 'plants-only' calculation looks tighter but you cannot reach the back row. Aisles are the second-largest space cost after fruiting plants.
- Forgetting vertical growth. Tomatoes need 4 to 6 ft of headroom; a greenhouse with a 5 ft 6 in roof at the side cannot grow tall fruiting plants near the walls.
- Maximizing density. Crowded greenhouses get fungal problems fast. Air circulation needs space; a slightly oversized greenhouse outperforms a maxed-out one for the same plant count.
- Picking glass for the first greenhouse. The cost gap between hoop and glass funds 5 to 10 years of layout iterations. Build cheap first, then permanent once you know what works.
- Building too far from a water source. Hand-watering 100 sq ft daily is fine. 300 sq ft daily becomes work. Plumb a hose bib or rain barrel within 25 feet of the greenhouse door.
Practical note
The calculator gives you the smallest greenhouse that fits your plant mix; in practice, most home gardeners want 20 to 40 percent more area for trial-and-error, season extension trays, and a small workbench. Sizing up one notch (say, from 10 x 12 to 10 x 16) usually adds 100 to 200 dollars on a hoop house and pays for itself the first time you want to overwinter peppers or start trays for the next season.
FAQ
What size greenhouse do I need for a typical home garden?
A 10 by 12 foot greenhouse (120 sq ft, 11 m²) covers most residential setups: 6 to 8 tomatoes, 4 to 6 peppers, a row of leafy greens, and a herb tray. For starts only (no full-grown plants), a 6 by 8 lean-to (48 sq ft, 4.5 m²) handles 200 to 300 seedlings. Calculate by your actual plant counts in this tool for a precise number.
How much space does each plant need?
Leafy greens (lettuce, kale, spinach) need about 1.5 sq ft per plant. Herbs (basil, parsley, cilantro) need about 0.75 sq ft. Fruiting plants (tomatoes, peppers, eggplant) need 4 to 6 sq ft when grown to full height. Vining plants (cucumbers, melons) need 6 to 9 sq ft sprawled or 2 sq ft on a vertical trellis. Add aisle space (24 to 30 inches typical) on top of the plant footprint.
Hoop house vs glass greenhouse, which is better for a beginner?
Hoop houses cost $1 to $3 per sq ft installed (using PVC, conduit, or galvanized steel hoops with poly film), last 3 to 5 years per film replacement, and are easy to scale or relocate. Glass greenhouses cost $25 to $50 per sq ft, last 20+ years, and look permanent. For a first greenhouse most beginners are better served by a hoop house, the cost gap funds 5 to 10 years of failed experiments. Glass makes sense once you know the layout works and you want a permanent structure.
Can I put the greenhouse against my house wall?
Yes, that is a lean-to greenhouse and it has real advantages: existing wall provides thermal mass, half the structure cost is eliminated, water and electricity reach are shorter, and the wall blocks one direction of cold wind. Best on a south-facing wall (north-facing walls in the southern hemisphere) for maximum sun. Limitation: width caps at about 8 to 10 feet before access becomes awkward, and the wall can shadow the back row in winter.
Does the calculator account for vertical growing?
Partially. The 'vining (trellised)' option assumes 2 sq ft per plant of footprint with vertical trellis support, which is the realistic compromise for tomatoes, cucumbers, and squash on a string trellis. Hanging baskets, tiered shelf systems, and full vertical farming towers are not modeled, those can multiply effective growing area 2 to 4x but require more attention. Use the calculator for the floor footprint, then plan vertical additions on top.
What about utilities and access space?
The calculator does not break out specific space for a potting bench, water barrel, or storage. Plan to add 10 to 20 sq ft for these on top of the plant-and-aisle estimate. Door swing also matters: French double doors need 5 to 6 ft of clear interior space; sliding doors need almost none. The estimate gives you the growing area; the bench, barrel, and pathway are extra.