Waist 66, will it be big to wear waist 70?

Yes The waist size of the same person should be the same as that of trousers, or there is not much difference. For a person with a waist circumference of 66, pants with a waist circumference of 70 will be a little loose, which will affect comfort and aesthetics. Waist circumference refers to the size after a circle around the natural waist, which is a common body size standard.