Calculate how much paint you need before you buy it. Be generous with your calculations and never underestimate.

The porosity, texture and existing colour of a surface affect the amount of paint required to cover it, highly porous surfaces absorb a considerable amount, especially when priming. Similarly, decorative surfaces like rough cast, embossed papers and textured coatings can be very thirsty, perhaps doubling the amount you might expect them to take. Two or three under coats may be needed to cover a strong colour and, when working outside, always allow for at least two topcoats for good protection against the weather.

To calculate the area of a large surface, break it down into smaller parts. Multiply the height by the width of each part and add all the totals together to get the final area. For windows with a fair number of mouldings and window bars, multiply the height by the width and count it as a solid area. For flat metal windows, deduct 25 per cent from the figure.

To find the area of a moulded door, multiply height by width and add 25 per cent.

Most paint tins indicate average coverage for the amount in the container. You can also use the following table as a general guide.