Yes, that is what flat rate (both domestic or international) means. Having had a mail/packaging store for 29 years, may I add a word of caution. Please lay a piece of plastic on the bottom of the box slightly up the sides. Even though the box feels coated, it will find moisture everywhere and suck it in. I did not like to enclose items within bags because they could not breathe and could develop a smell very quickly. Also, put a label on the inside of the box in case something happens to the outside. Before you use the flat rate box, check the usps.com website and see if there isn't a cheaper way to ship, remembering to get it into as small a box as possible because it will be charged dimensional vs. actual weight.