A striped cushion next to a floral throw next to a checked rug sounds like a recipe for a busy room. Often it works beautifully, and the reason is not luck. Patterns get along when they differ in one particular way: scale, meaning how big the repeat is. Get that right and the rest is easy.

Why patterns clash, and why they don't

Your eye reads a pattern as a texture from a distance. Two patterns with the same size of repeat compete: both are shouting at the same volume. Give one a big repeat, one a medium repeat and one a small repeat, and your eye can sort them into a loud one, a middle one and a quiet one. That is why a wide stripe, a medium check and a tiny dot can sit together on one sofa.

The second thing that holds a mix together is a shared colour. If every pattern contains the same sage green, or the same warm clay, they read as one family even when the shapes are different.

Try it: build a mix on a sofa

The slider labels use centimetres on screen, so think of them as the size of one repeat on a cushion or rug. On a real rug the repeat is much bigger, and the same ratios still apply.

The three-step recipe

1. Pick a shared colour. Choose one colour that is already in your room, such as the sofa, a curtain or a picture. Every pattern you add should contain a little of it.
2. Vary the scale. One large repeat (a wide stripe, a big check or a bold leaf), one medium and one small. A common designer rule of thumb is to keep each step roughly two to three times the size of the one below, but it is a guide, not a law.
3. Give the eye a plain place. Leave the biggest surface, often the sofa or the bed, plain, and add a few solid cushions or a solid throw between the patterns.

Breaking the rules on purpose

Same-scale mixes can work when the patterns are very similar in feeling, such as two soft stripes in related colours. Dark, saturated colours also shout louder than pale ones, so a small dark pattern can outweigh a big pale one. If something looks off, swap one pattern for a plain fabric before you change everything.

Use what you already have

Cosy does not mean buying more. Before shopping, lay out the cushions, throws and tablecloths you own on the sofa and try the recipe. Often swapping cushions between rooms, or borrowing a throw from the bed, is enough. Second-hand and charity shops are a good place to find an odd pattern in the right colour for a few euros.

What to measure before you add anything

Patterns look bigger in a room than on a screen or a small sample. Take a photo of your sofa and walls, hold the fabric sample next to them in daylight and in the evening, and look from the far side of the room, because that is where you will actually see it. For a rug, measure the floor space first (width and length in cm) so a large repeat is not chopped off at an awkward place.