Remember to leave a 5 cm gap around the fridge sides AND TOP to ensure that the heat exchange element gets enough air circulation to work properly. 10 cm is even better. Cutting a generous hole in the base of the cabinet and fitting a small fan to blow air through the hole will help the fridge work better too. Otherwise you’ll spend a lot of time defrosting the fridge and a lot of energy running it. Ikea has paper tape measures for free that are good for a limited number of uses, and you can write on them with a biro - eg width measurement and height measurement of cupboard.