The minimum label size that fits a postage insignia is 3 inches high by 3 1/2 inches wide. You can use sheet labels as long as the labels are large enough. On a letter-size sheet, this usually limits the quantity of labels to six (6) or fewer labels per sheet.
On envelopes, you must place date or amount correction indicia on the back side of the envelope at least 3/4 inch from the bottom edge and not on top of the envelope flap. On flats or parcels, the correction indicium must be placed next to the original indicium.
Caution! You must print any date and amount corrections with caution. The US Postal Service requirements specify that the postage must match the delivery (destination) address.
Label Size for Date or Amount Corrections: ...MORE