I am not sure how to measure this stamp
I found it at a sale
Thank you for submitting your item for appraisal. This appears to be US postage 2c Washington stamp, commonly called "Scott 634" according to the number in the stamps catalogue. This stamp was once part of the upper part of a plate block, possibly mid 1920s. Millions of these stamps were printed and sold with sometimes very slight variations, which an not be certified or graded online unfortunately.