Start with the light, not the colour chart

Every paint colour carries a light reflectance value, or LRV — a number between 0 and 100 that tells you how much light the dried paint throws back into the room. It is usually printed on the back of the colour card or tucked into the range's technical information, and it is the single most useful figure when you are choosing paint for a compact space. Anything in the seventies and above — soft whites, pale greys, gentle stones, chalky off-whites — will bounce daylight around a box bedroom, a galley kitchen or a narrow Victorian back room. Drop below 50 and the walls begin absorbing light rather than reflecting it. That is why a rich charcoal can look wonderful in a large, sunny sitting room and quietly oppressive in a room that is barely two metres wide.

None of that means you are condemned to magnolia for the rest of your days. It simply means light comes first and colour comes second.

Read the room's own light before you buy anything

A north-facing room receives cool, slightly blue daylight all year, which can make blue-based greys and cool whites turn flat and faintly grey on the wall. Warm those rooms up with whites that carry a hint of yellow, pink or cream. South-facing rooms get strong, warm light for most of the day and can comfortably take a cooler grey or a soft green without turning chilly.

Look outside as well as inside. A room overlooking a lawn or mature trees picks up green reflected light, which flatters greens and can make pinks look muddy. A room facing a red-brick terrace may catch a warm glow in the afternoon. Deep window reveals, a narrow window, or a neighbouring wall that blocks the sun will darken a room far more than any paint choice, so be honest about how much daylight actually arrives.

If the room is mostly used in the evening, judge your samples under the bulbs you will actually live with. Warm white bulbs around 2700K keep neutrals looking neutral; cooler, brighter bulbs will push anything with a yellow undertone towards a slightly soured tone.

Treat the ceiling and woodwork as part of the scheme

A stark brilliant white ceiling sounds like a safe default, but in a small room it can draw a hard line across the top of the walls and make the ceiling feel lower than it is. Instead, take the ceiling a shade or two lighter than the walls from the same colour card. It keeps the space feeling continuous rather than boxy.

Then consider colour drenching: painting walls, ceiling, woodwork and even radiators in closely related tones. In a small room this blurs the edges, so the eye no longer stops at the skirting board, and the whole space reads as one calm volume. It works particularly well in a downstairs cloakroom or small bathroom, where you are not relying on a pale ceiling to bounce light deep into the room.

If you do drench, keep skirting boards and architraves in the same family. Brilliant white trim against a deeper wall colour creates a hard-edged frame, and a frame is the last thing a narrow room needs.

Use stronger colour for depth, not for shrinking

Feature walls are the classic error in a compact room. Painting one wall a deep shade can make it feel as though it has physically moved closer. A better approach is to put the stronger colour where it adds interest without eating floor space:

• Inside a chimney breast alcove, or on the back wall of a shelving recess, where it reads as depth rather than bulk.
• On the wall you look at least often, rather than the one facing the door.
• Below a dado rail, so the lower third grounds the room while the upper two-thirds stays light and airy.
• On the far wall only, painted a shade or two deeper than the rest, to draw the eye through the space.

Whatever you choose, avoid dark borders wrapping the whole room. A continuous dark band around the top, bottom and sides of a small space closes it in quickly.

Test samples properly before committing to a tin

Colour cards lie. A postage-stamp square in a shop lit by fluorescents tells you almost nothing about how a colour will behave on your walls. Buy tester pots and paint two coats onto A2 sheets of lining paper, leaving a white border around the paint so you can judge it honestly. Tape the sheets up in different parts of the room — the corner that gets least light, the wall beside the window — and live with them for several days.

Look at the samples at breakfast, at midday and after dark with the lamps on. Prop them behind the sofa, next to the flooring and beside any curtain fabric. This is when undertones reveal themselves: put two similar neutrals side by side and the yellow, pink or green hiding inside them will suddenly jump out. Two or three tester pots cost a fraction of repainting a whole room because the colour went wrong at 4pm in November.

Finishes, sheen and a few practical details

Matt emulsion is the kind choice for small rooms because it softens imperfections — and small rooms tend to have filler marks, uneven plaster and old picture hooks. Matt also absorbs a little light, though, so in a genuinely dark room a washable matt or a low-sheen finish will reflect more back and is easier to wipe down. A mid-sheen finish is ideal in a small bathroom or kitchen, where it bounces light off the walls and copes with steam and splashes, but avoid high gloss on uneven walls: it highlights every lump.

A few last things worth doing. Buy all your tins in one go so they come from the same batch, and if you are using more than one tin in a single room, mix them together in a large bucket before you start — it guarantees an even finish. Keep a little leftover paint in a labelled jar for touch-ups, and make a note of the colour name and finish somewhere you will find it again. Small rooms reward a bit of planning more than any other space in the house, and getting the light right is where that planning starts.