How it works

Choose the calculator for your project and country, then enter the measurements it asks for. Use the units shown beside each field and check the help notes if you are unsure what to measure.

Select the options that match your plan and choose Calculate. The result summarises an estimated quantity to buy, followed by the calculation details and any shopping-list information the tool supports.

Before using the estimate, read the worked example, method, sources, assumptions and safety notes below the calculator. Change optional allowances to fit your layout, and confirm the selected product and quantity with your supplier.

Calculators are planning aids. They do not inspect a site, decide whether a design is safe or replace product instructions, permits or qualified advice.