Does a 5×7 count as a letter?
In many cases, yes. A 5 by 7 inch envelope is within the usual maximum dimensions for a First-Class letter, as long as the longest side and shortest side stay within USPS letter limits and thickness and weight stay within letter limits. Our calculator uses your length, height, and thickness to decide whether you are still in letter territory or have moved to a large envelope (flat).
If your piece is too thick—think bulky cards, pins, or layered paper—you can exceed the quarter-inch letter thickness limit even when the outer envelope still says 5×7 on the label. That is why we ask for thickness, not just the envelope size printed on the box.
How much postage for a 5×7?
Postage depends on weight and on whether the mail is non-machinable. A lightweight card might be one ounce and need a single Forever stamp. Add inserts or heavier paper and you may jump to two ounces—Forever plus an additional ounce stamp. If your envelope is square (same width and height), check the square envelope box because surcharges apply.
Weddings, photos, and invitations
5×7 is a popular size for invitations and photo mailers. Those mailings often use heavier stock or liners, which pushes weight up faster than people expect. Weigh the finished envelope, not just the paper. If you add wax seals or ribbons, you may also affect machinability; rigid or lumpy mail can trigger non-machinable handling even when weight looks fine.
When a 5×7 is not priced as a letter
If any letter limit fails—weight over 3.5 oz, thickness over 0.25 inches, or dimensions outside allowed maximums—USPS may classify the piece as a flat. This tool will tell you when that happens so you do not apply letter-stamp math to a flat. Flats have their own retail structure; we will add flat pricing in a future release.
Using this page with your numbers
Presets use 7″ length and 5″ height to match a common 5×7 orientation. If your envelope is rotated, swap length and height only if it changes which side is longer; the calculator cares about the actual measurements, not the wording on the envelope. Enter the true thickness at the thickest point, then read the total postage and the “stamps to use” line for a clear answer tailored to your piece.
Retail packaging sometimes labels products “5×7” even when the usable interior is smaller; that does not change postage rules, but it does affect whether your contents fit without bulging. Bulges increase thickness unevenly. Measure where the envelope is thickest after you insert the card or letter. If you stack multiple cards, you may move from one ounce to two ounces even though each card felt light on its own. The calculator is only as accurate as the numbers you enter, so spend thirty seconds on measurement before you trust the output.