If you use an electric rice cooker, or the ‘absorption’ method in a saucepan, it is important to measure the water (or other liquid) accurately.
You can assume you will need, for example, 280 ml/10 fl oz/1¼ cups of water to 225 g/8 oz/1 cup of rice. If your rice is a dry variety, like Basmati, or if you like it rather soft, add a little more water; up to 340 ml/12 fl oz/1½ cups of water to 225 g/8 oz/1 cup of rice. The same quantity of brown rice may require 427 ml/15 fl oz/ nearly 2 cups of water.