Bassinet Size Mattress Dimensions are generally 16 inches wide x 32 inches long. Additional bassinet bed dimensions can be 13 inches by 29 inches, 17 inches by 31 inches, 15 inches by 30 inches, etc., depending upon the manufacturer. These are fairly standard Bassinet bed measurements. Bassinet Mattress depths can vary, usually 2 to three inches thick Of course, some manufacturers may build to their own size. Extreme care must be observed with Bassinet mattresses and bedding.