The general rule of thumb for cooking rice in a rice cooker is to use a 1:1 ratio of rice to water. So, to cook one kilogram (1000 grams) of rice, you would need 1000 milliliters (ml) or 1 liter of water.
When it comes to the size of the rice cooker, you'll want to consider the cooked rice's final volume and choose a rice cooker that can accommodate that amount without overflowing. Keep in mind that rice expands during cooking, roughly doubling in volume. So, one kilogram of uncooked rice will yield approximately two kilograms of cooked rice.
As a result, a rice cooker with a capacity of around 2 liters should be sufficient to cook one kilogram of rice. This will provide enough space for the rice to expand and cook properly without spilling over. It's always a good idea to choose a slightly larger capacity than you need to prevent any potential messes and ensure the rice cooks evenly.