Interior design programmes have long been a staple of daytime TV, and their popularity has lead to an increased demand for designers. To succeed as an interior designer you need to be creative and have a good sense of style, but you also won’t get far without some maths.

Nearly every aspect of interior design requires mathematical thinking. Can you coat a whole room with just one can of paint? Do you have enough material for a new set of curtains? Answering these questions is simple when you understand geometry and measurement.

### Paint by numbers

Painting a room is easy – just grab a brush and get to work. A little more thought is needed if you want to do the job properly though. An interior designer must calculate the exact amount of paint they need to use. Otherwise, they might buy too much and waste money, or not buy enough and run out! One litre of paint will cover around 10 square metres, so designers use this conversion rate to work out how much they need.

Suppose you wanted to paint the walls and ceiling of a room. You would first need to work out the total surface area of the room, excluding the floor. That’s not too difficult if the room is a cuboid, but most are irregularly shaped. You can use geometry to carve these shapes up in to ones that are more basic, making them easier to manage. If a room has curved walls, knowing how to calculate the surface area of cylinder will come in handy too.

What about the doors and windows? You also have to work out the area for those, and subtract them from your total. Not every surface is a simple rectangle either. Windows can be round and doors can be sloped, meaning you have to use the formulae for the areas of a circle and triangle. When it comes to painting, calculations are just as important as picking colours.

### Is it curtains for you?

Interior designers must be able to size up a room as soon as they enter. This means designers need to know how to make accurate size estimations in order to get to work as soon as possible.

Imagine that a client wants a new set of curtains for their living room. While they excitedly talk fabric patterns, you’re estimating the size of the windows, how much material you’ll need, and what the cost will be. With a rough figure in your head, you’re ready to go straight away. That’s much more impressive than messing about with a tape measure.