Deck your roof with the correct number of boards using our calculator
Whether you're using plywood or OSB, simply entering your roof area and chosen sheet material size will present you with the number of boards needed (rounded up to the nearest full sheet) plus an additional result that includes 10% wastage.
Plywood Sheet Calculator
Number of Plywood Sheets Required: 0
Including 10% Wastage: 0
OSB Sheet Calculator
Number of OSB Sheets Required: 0
Including 10% Wastage: 0
How to Use the Calculators
- Select the type of sheet material (Plywood or OSB) from the 2 calculators.
- Choose the sheet size you plan to use from the dropdown menu.
- Enter the total roof area in square feet or square metres.
- Click the "Calculate" button to see how many sheets you will need.
Calculator checked on By Jamie
Calculations Used
| 4' x 8' (32 sq ft / 2.973 sq m) |
Number of Sheets = Roof Area (sq ft or sq m) ÷ Sheet Size (32 sq ft or 2.973 sq m) |
| 4' x 12' (48 sq ft / 4.459 sq m) |
Number of Sheets = Roof Area (sq ft or sq m) ÷ Sheet Size (48 sq ft or 4.459 sq m) |
| 8' x 8' (64 sq ft / 5.946 sq m) |
Number of Sheets = Roof Area (sq ft or sq m) ÷ Sheet Size (64 sq ft or 5.946 sq m) |
What is Roof Sheathing?
Roof sheathing (or sheet decking) is a layer of material that is attached to the roof's structural frame, providing a base for the roofing materials, such as shingles or tiles.
It plays a critical role in the overall stability and weather resistance of the roof. Common materials used for roof sheathing include plywood and OSB (Oriented Strand Board).
Plywood vs. OSB: Which is Better?
Plywood
- Strength and Durability: Plywood is known for its superior strength and stiffness. It is also more resistant to impact damage and has a higher tolerance for moisture than OSB, particularly if it's of high-quality grade.
- Moisture Resistance: Plywood generally handles moisture better than OSB and is less likely to swell, warp, or delaminate when exposed to water. This makes it a better choice in regions with high humidity or where the roof might be exposed to moisture during construction.
- Cost: Plywood tends to be more expensive than OSB, which could be a deciding factor for those working within a tight budget.
OSB
- Cost-Effective: OSB is a popular choice for budget-conscious projects as it is less expensive than plywood.
- Consistency and Availability: OSB is manufactured using smaller, more uniform wood chips, which can be sourced from younger, faster-growing trees. This not only makes OSB more environmentally sustainable but also often results in a more uniform product with fewer voids and inconsistencies compared to plywood.
- Moisture Sensitivity: OSB is more sensitive to moisture. When it gets wet, it can swell more significantly along the edges than plywood, and it may take longer to dry out.
Why You Should Include a Waste Factor
When cutting and fitting roof sheathing, it's inevitable that some material will be wasted.
To ensure you purchase enough material, it's wise to include a waste factor in your calculations. Typically, this waste factor can be around 10%, but it might be higher for complex roofs with more cuts, such as hip roofs.
Our calculator provides you with an additional figure that includes a 10% wastage allowance.
Frequently Asked Questions
Can I use the calculator for both residential and commercial roofing projects?
Yes. You can input any roof dimensions, and the calculator will help you determine the amount of sheathing required for both residential and commercial projects.