Greenhouse Calculator: 11 Panels for a 10x8 ft House

What does greenhouse glazing needed 11 panels mean?

It means eleven panels glaze a 10 ft by 8 ft greenhouse with 6 ft walls, with room for cuts. The floor is 80 square feet, the walls are 216 square feet, since twice the sum of the sides, 36 ft of perimeter, times 6 ft of height is 216, and the roof is 100 square feet, since the floor times the 1.25 slope allowance is 100; walls plus roof are 316 square feet of glazing. One 4 ft by 8 ft panel covers 32 square feet, so the exact need is 9.88 panels, and with 10% waste for cuts and breakage that becomes 10.87, rounded up to 11 whole panels because panels are sold by the panel, not by the fraction.

Output · formula · meaning

Three things to check before you trust the number

First, check the roof factor you are actually building: 1.25 is a planning allowance for a pitched roof, not a measured pitch, and a steep roof wants more glazing than a shallow one, while the walls never change. Second, check the panel size you are actually buying: 4 ft by 8 ft is the common panel, but a smaller panel covers less glazing each and raises this greenhouse past 11 panels, while the glazing area never changes. Third, judge the waste honestly: greenhouse panels break and are cut to fit, so a greenhouse with many small panes can want 15%, since every pane takes a cut. Doors, vents and the foundation are counted separately — see the garden bed calculator for the beds inside a greenhouse like this one.

Worked example

10 ft long, 8 ft wide, 6 ft walls, 10% waste. Floor: 10 × 8 = 80 sq ft. Walls: 2 × (10 + 8) × 6 = 216 sq ft. Roof: 80 × 1.25 = 100 sq ft. Glazing: 216 + 100 = 316 sq ft. Panels exact: 316 ÷ 32 = 9.88. With waste: 9.88 × 1.10 = 10.87, rounded up to 11 panels. In practice that means buying 11 panels, and expecting the last one to go on cuts and breakage. If the same greenhouse had 7 ft walls instead, the need would rise to 13 panels, but the floor would be identical.

Every branch, checked

With a 12 ft long greenhouse instead of 10 ft, the glazing rises to 360 sq ft and the need to 13 panels. With a 10 ft wide greenhouse, the glazing rises to 365 sq ft and the need to 13 panels, since the floor and the roof grow with the width. With 7 ft walls, the glazing rises to 352 sq ft and the need to 13 panels. With 5% waste, the exact need stays 9.88 panels and the buy stays 11 panels, since 9.88 × 1.05 is 10.37 and still rounds up to 11. Length, width, height and waste each move the order on their own, so a wrong height figure is as costly as a wrong measurement.

The reverses, worked backwards

The length behind 11 panels is 10 ft: at 8 ft the need is 10 panels (8 ft × 8 ft greenhouse, 6 ft walls, 272 sq ft glazing, 8.5 panels exact, 10% waste); at 12 ft it is 13 panels (12 ft × 8 ft greenhouse, 6 ft walls, 360 sq ft glazing, 11.25 panels exact, 10% waste). The height behind 11 panels is 6 ft: at 5 ft the need is 10 panels (10 ft × 8 ft greenhouse, 5 ft walls, 280 sq ft glazing, 8.75 panels exact, 10% waste); at 7 ft it is 13 panels (10 ft × 8 ft greenhouse, 7 ft walls, 352 sq ft glazing, 11 panels exact, 10% waste). The waste behind 11 panels is 10%: at 5% the need is 11 panels (10 ft × 8 ft greenhouse, 6 ft walls, 316 sq ft glazing, 9.88 panels exact, 5% waste); at 15% it is 12 panels (10 ft × 8 ft greenhouse, 6 ft walls, 316 sq ft glazing, 9.88 panels exact, 15% waste). Each reverse moves one input and holds the rest, so the step is exactly one dimension, height or waste change.

What the defaults assume

The defaults assume a 10 ft by 8 ft rectangular greenhouse, 6 ft walls, a 1.25 roof slope allowance, 4 ft by 8 ft panels, and 10% waste for cuts and breakage. They do not assume doors, vents, a foundation or a measured roof pitch — a greenhouse with a wide door counts its door glazing separately, and a steep roof is measured by its pitch, not by the allowance.

Who uses this

• A gardener glazing a greenhouse: the 11-panel order settles the yard call before the first panel is cut.
• A DIY builder framing a greenhouse: the same maths on the greenhouse alone gives the glazing, not a whole garden.
• A nursery grower budgeting a house: greenhouse size, wall height, waste — the quote follows the same steps, and the waste line shows why breakage is priced in.
• A contractor quoting a job: the greenhouse size off the plans, multiplied out, gives the panel line on the quote.

Accuracy & limitations

The arithmetic is exact for the inputs entered; the judgement is the roof factor and the waste. Real greenhouses have doors, vents and panes of many sizes, and the panel on the pallet overrides any planning figure; a greenhouse measured gross over-orders, and a waste figure read off a plain house under-orders one cut into small panes. Treat 11 panels as the planning order for a 10 ft by 8 ft greenhouse at 6 ft walls and 10% waste, and allow 15% for a house cut into small panes.

Cite this calculator

Bright Side Kit, “Greenhouse Calculator: 11 Panels for a 10x8 ft House”, https://brightoolbox.com/greenhouse-calculator/, accessed 3 November 2026. Students and researchers: cite the calculator name, the page URL and the date you used it, and quote the defaults (10 ft × 8 ft greenhouse, 6 ft walls, 10% waste) so the 11-panel result can be checked.

Frequently asked questions