Greenhouse Area Calculator
Find your greenhouse's floor area and total covering (poly film) area for a tunnel or gable-roof design — just enter the dimensions.
Common Polyhouse Sizes
Typical floor area ranges seen in commercial polyhouse projects.
| Scale | Typical Floor Area |
|---|---|
| Small / trial | 100 – 500 m² |
| Small commercial | 500 – 1,000 m² |
| Medium commercial | 1,000 – 4,000 m² |
| Large commercial | 4,000 m²+ |
How This Calculator Works
From basic dimensions to gross covering area, for either roof shape.
Why Greenhouse Area Calculations Matter
Getting greenhouse (polyhouse) area right feeds directly into two of the biggest cost decisions in a protected cultivation project: how much covering material (typically UV-stabilized polyethylene film) to buy, and how much usable growing floor space the structure actually provides. Covering material is priced by area and typically sold in fixed-width rolls, so an accurate area estimate — including a sensible wastage allowance for overlaps and future patch repairs — avoids both costly over-ordering and disruptive mid-project shortfalls.
This calculator handles the two most common commercial greenhouse shapes: the tunnel (Quonset), with its continuous semi-circular arched roof, and the gable-roof design, with two flat, angled roof panels meeting at a central ridge.
Tunnel (Quonset) Greenhouse Formula
A tunnel greenhouse's cross-section is a semicircle, with the radius equal to half the greenhouse width. The roof covering area is the arc length of that semicircle multiplied by the greenhouse's length, and the two semi-circular end walls add up to one full circle's worth of area.
Roof Area = π × (Width ÷ 2) × Length
End Wall Area (both ends) = π × (Width ÷ 2)²
Gable-Roof Greenhouse Formula
A gable roof's two panels are each a rectangle whose width is the "slant length" from the side wall to the ridge, calculated using the Pythagorean theorem from half the greenhouse width and the height difference between the ridge and the side wall.
Slant Length = √[(Width ÷ 2)² + (Ridge Height − Side Wall Height)²]
Roof Area = 2 × Slant Length × Greenhouse Length
End Wall Area (both ends, incl. gable triangles) = 2 × [(Width × Side Height) + (0.5 × Width × (Ridge Height − Side Height))]
How to Use This Calculator
- Choose your greenhouse shape — tunnel or gable roof.
- Enter length and width for either shape.
- For gable roofs, also enter side wall height and ridge height.
- Set a wastage/overlap allowance percentage — 10% is a common general default.
- Tap "Calculate Greenhouse Area" to see floor area, roof covering area, end wall area, and total covering material needed.
Choosing Between Tunnel and Gable Designs
- Tunnel (Quonset): Generally simpler and cheaper to construct, with good structural strength against wind due to its curved shape, though headroom near the sides is more limited.
- Gable roof: Offers more usable headroom throughout and can better accommodate taller crops or overhead equipment like hanging trellis systems, but typically costs more to build due to the more complex frame.
Tips for Ordering Covering Material
- Always add a wastage allowance. 10–15% extra covers seam overlaps, installation cutting waste, and future patching material.
- Check roll widths before ordering. Poly film typically comes in fixed roll widths, which may require the covering to be pieced together with overlapping seams rather than a single continuous sheet.
- Consider UV-stabilized film. Standard polyethylene degrades quickly under continuous sun exposure; UV-stabilized film typically lasts several years longer.
- Plan for replacement cycles. Most greenhouse film needs replacement every 3 to 5 years depending on climate and film quality — factor this into long-term cost planning.
Final Thoughts
A few accurate dimension inputs go a long way toward avoiding both wasted covering material and unexpected shortfalls mid-installation. Use this calculator at the planning stage of any new greenhouse project, and recalculate whenever you're evaluating design changes like widening the structure or switching from a tunnel to a gable-roof design.
Frequently Asked Questions
Multiply the greenhouse's length by its width to get the floor area in square metres, regardless of whether the roof is tunnel-shaped or gable-shaped, since floor area only depends on the base footprint.
For a semi-circular tunnel, the roof covering area equals the arc length (half the circumference of a circle with radius equal to half the width) multiplied by the greenhouse length, plus the two semi-circular end walls.
A tunnel (Quonset) greenhouse has a continuous semi-circular arched roof, while a gable-roof greenhouse has two flat, sloped roof panels meeting at a ridge, similar to a traditional house roof shape.
A curved (tunnel) roof and an angled (gable) roof of the same floor footprint have different total surface areas to cover, since the curved arc length and the two angled roof slant lengths are calculated differently even when the base width is identical.
It's common practice to add 10 to 15 percent extra to the calculated covering area to account for overlaps, wastage during installation, and future patch repairs.
Ridge height depends on the crop and ventilation needs, but many polyhouse designs use a ridge height noticeably higher than the side wall height to improve air circulation and accommodate tall crops, commonly in the range of 4 to 6 metres for commercial structures.
No, this calculator gives the total gross covering area based on the greenhouse's overall dimensions. Doors, vents, and other openings are typically a small fraction of total area and are usually accounted for separately during actual material ordering.
Many small commercial polyhouse projects start in the range of 500 to 1,000 square metres of floor area, which is large enough for meaningful production while keeping initial investment more manageable than very large structures.