How many 4′ x 8′ sheets of plywood do I need? This calculator does not simply divide the total square footage by 32. It figures how many pieces long, then how many wide. Use the drop downs below to select a length in feet. Then do the same thing for the width. For more complicated shapes, see the instructions below.

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Solving for the number of sheets of plywood necessary for more complicated shapes requires at least some estimating. Follow theses guidelines for a closer estimation.

- For a shape like a triangle (gables and hips), trapezoid (hip side with the ridge), or trapezium (gable roof with a valley); find the average length by measuring at the center of the width. Then add at least four feet for waste. Remember, the longer the cut, the more the waste.
- For a shape like a circle, pentagon, hexagon, or octagon, find 25% of the width and measure the length at that point. Add at least six feet for waste.
- No calculator can tell how much waste will be on each run plywood. That is dependent on the lay out and where it ends with the plywood. Sometimes there is no waste such as on a run 32′ long. It will take four sheets. A run 31′ long will also take four sheets with a 12″ piece left a remainder. If the joists or rafters are on 12″ centers, there may be a use for this waste, otherwise it will have to be discarded. A good rule of thumb is to add 10% to the number of pieces to allow for waste and mistakes.