1. A wall colour you don’t like is hard to live with and as there are so many different colours and finishes to choose from, it’s important to try a new paint first.
It is a good idea to apply a little of a new colour to each wall, so you get the full effect and can see how it looks at different times of the day. Printed colour charts aren’t accurate, so don’t rely on them, and the same is true of paint colours viewed online - always try the paint in the room it’ll be used in.
2. Once you’ve found an emulsion you like, you’ll need to work out how much to buy. The paint tin will have information on coverage, and you can use an online paint calculator to work out how much paint is needed per room. These calculators take into account things like the size of the walls, windows and doors, but not the type of emulsion you’re using or the state of the walls themselves.
3. As soon as you start applying an emulsion, you’ll be able to see how well it covers and get an idea of how many coats you’ll have to do. The quality of the emulsion will affect the number of coats, as will the state of the walls. More paint will be needed to cover textured wallpaper and lumpy and bumpy walls than smooth ones (new plaster should be sealed first to make it less absorbent). Some emulsions cover better than others and in my experience, budget ones rarely cover well. It’s worth paying more for a good quality paint that provides excellent coverage than scrimping and paying for it later.
4. The colour you use can also affect how much emulsion you need. Pale colours may not cover as well as dark ones, and if you’re painting new plaster with pale emulsion, there may be patches you can’t cover easily - use a stain-block paint or a basecoat emulsion on these. Basecoat emulsions, which are white and cover better than most standard emulsions, are useful if the emulsion you’re using isn’t covering well. If you’re painting over dark walls with a pale colour, for example, you’ll save time, effort and paint by applying a basecoat first.
5. It’s obviously better to have too much emulsion than not enough, as long as you can return it - most DIY stores will refund unused tins, although usually not from paint-mixing machines (unless faulty). Sometimes, the same colour can change slightly between batches of paint, especially with paints that use natural pigments, so not buying enough in the first place can be disastrous.