The size of your greenhouse film isn't necessarily determined by just the length and width. You must account for the total length of the pipes you are using to complete a hoop, and also your end walls.
How to measure for greenhouse film
Start with the width.
Throw a rope over the greenhouse, take the end of the rope to the ground. Have a friend mark the rope at the other side ground level.
Then, stretch the rope straight and measure to the mark. This will account for the arch's radius accurately.
Add 4' to the actual width for safety and/or roll-up sidewalls.
Getting the total length by measuring the height (x2) + structure length:
Here are details on how to measure the size of the shade cloth you may need:
For shade cloth, measure from hip board to hip board & add 2' extra for each the length and width.
These are the charts that we use for processing our greenhouse kits. Note the difference in sizes between the 1st layer and 2nd layer (optional).
Shop our selection of DIY greenhouse kits, plastic film and shade cloth at our shop. On our product page for plastic film, you can see a complete chart of recommended sizes for hoop houses according to the width and length of your structure.