1. Find the roof run
Use the measured over-hoop distance, a circular-arc calculation, or two gable slopes. Straight sidewalls are included in the geometric methods.
HOOP HOUSE FILM ORDER PLANNER
Greenhouse Plastic Size Calculator
Turn field measurements into a main cover cut, optional end-wall pieces, a roll-width fit check and the linear length to order, without assuming every greenhouse has the same arch.
Method and edge cases reviewed
STRUCTURE AND FILM
Build the cover order
1. Measure the structure
Run a flexible tape or rope from ground to ground over the outside of the frame.
2. Add fastening and end allowances
These are per-side and per-end values. Enter the material needed for lock channel, baseboards, buried edges, tensioning and handling according to your fastening system.
3. Match the supplier's roll
MINIMUM SEAMLESS WIDTH
24ft minimum film width
Fits the selected roll0 ft of width remains beyond the calculated main cover.
- Main cover cuts
- 1 x 24 x 50 ft
- End-wall cuts
- Not included
- End-panel packing
- Not included
- Raw roll length
- 50 ft
- Length to order
- 50 ft
- Purchased film area
- 1,200 ft²
- Rectangular offcut
- 0 ft²
- Cost at entered rate
- Add a price
Order length assumes the main cover runs across the fixed roll width. Confirm the film's fold, layer orientation and sell-by increment with the supplier.
FIELD-TO-ROLL CHECK
Review the cover and cut plan
This diagram summarizes the selected dimensions. It is not a scale cutting template and does not replace a supplier cut sheet.
THREE MEASUREMENT METHODS
Choose the method that matches what you can verify
| Method | Measure | Use it when | Important limitation |
|---|---|---|---|
| Measured over hoops | Outside ground-to-ground distance over the installed frame | The frame exists or one finished hoop is available | Keep the tape on the same path the film will follow |
| Circular segment | Base width, straight sidewall height and peak height | The roof is a known circular arc | Do not use for Gothic, multi-radius or irregular bows |
| Gable roof | Base width, eave height and ridge height | Both roof slopes are straight | Curved shoulders or roof vents need direct measurement |
Rope method
Throw a non-stretch rope over the outside of a representative hoop, mark both ground points, lay it flat and measure between the marks. Repeat once to catch routing mistakes.
How the film order is calculated
2. Build the main cut
Side allowances are added twice to the roof run. End allowances are added twice to the greenhouse length.
3. Pack the roll
Each main layer consumes one cut length. Optional end rectangles are tested upright and rotated across the chosen roll, then the total is rounded to the supplier's increment.
Main cover width
roof run + (2 x side allowance)
Main cover lengthgreenhouse length + (2 x end allowance)
Round roof radius(rise squared + half-span squared) / (2 x rise)
Order lengthround up (main cuts + packed end cuts) to supplier increment
Field references behind the workflow
- ACF Greenhouses film sizing example - demonstrates measuring bow length with a tape or rope and adding handling allowance.
- Utah State University Extension low-cost high tunnel guide - specifies a 24-foot-wide by 50-foot-long cover for a 14-by-42-foot tunnel and describes side and end attachment allowances.
- Americover greenhouse film guide - advises adding extra film beyond the measured roof and sides for fastening.
- Penn State Extension high tunnel production - distinguishes typical single-layer high-tunnel covers from inflated double-layer greenhouse systems.
Allowance is installation-specific. The calculator does not silently replace your supplier's instructions with one universal extra-foot rule.
Confirm these items before ordering film
- Measure the completed outside frame, including straight sidewalls, hip boards or the exact fastening path.
- Confirm that the selected roll width is the usable unfolded film width, not a folded package dimension.
- Ask whether the supplier sells exact lengths or rounds to whole feet, meters or preset roll lengths.
- Do not add separate end-wall panels when the planned main-cover overhang will supply those panels.
- For a double-inflated roof, confirm how the two layers, inflation hardware and end seals are installed.
- Use the structure manufacturer or an engineer for wind, snow, hoop spacing, bracing, foundations and fastening design.
Greenhouse plastic sizing questions
How wide should greenhouse plastic be?
The minimum seamless width is the ground-to-ground distance over the roof and sidewalls plus the attachment allowance at both sides. Measure over the actual frame whenever possible.
Why is greenhouse width not enough to calculate the film?
The film follows the curved or sloped roof rather than crossing straight over the base. Two structures with the same base width can have different roof runs.
Should end-wall plastic be added separately?
Add separate end rectangles only when the main cover will not provide enough end overhang or when the construction method calls for separate panels. Otherwise the same material may be counted twice.
Does double layer mean doubling the order length?
Yes for two separate full main-cover layers. Some high tunnels use one layer, while inflated greenhouse systems may use two; follow the system specification.
Can two pieces be seamed when the roll is too narrow?
Field seaming changes water shedding, strength and installation behavior. This calculator flags a narrow roll and reports the seamless width instead of assuming a seam is acceptable.
Does the calculation include doors and vents?
The optional end walls are purchasing rectangles. Door and vent cutouts usually become offcuts during installation, so they are not subtracted from the amount ordered.