Sizemaven

Sizemaven tells you which size to buy, then shows real products in that size. Enter a few numbers, such as your room size, your height and weight, your child's foot length or your dog's chest. The tool gives one size, explains the rule behind it, draws it to scale and names the source, such as a maker's own size chart. Under the answer are products on Amazon whose listings confirm that size, within your budget. It is free, with no account, and covers 18 product types.