For each roof shape, you’ll see an isometric representation with letters and the formula. The letters of the isometric representation correspond to the corresponding formula.

The basic rules of calculation apply:

• Multiplication and division go before addition and subtraction.
• Calculate the letters in brackets first, before filling out the formula.

The letters indicate the dimensions for the calculation. Depending on the type of calculation you make, this can be internal or external measurements.

Do you have internal dimensions, and do you want to calculate the content of the roof on the outside (gross volume)? Add the possible thickness(es) of the (roof) construction to the measured internal dimensions. Do this before filling in the formula.

All roofs and formulas are for calculating roofs without overhang. The moment a roof has an overhang, pay attention if you need to add the construction thickness of the roof.

If necessary, ask a professional for help.