Use case · USPS prices effective July 12, 2026 · Updated October 2, 2026
How much are USPS Flat Rate boxes?
Direct answer
A Priority Mail Flat Rate box is one price to any U.S. zone if the item fits, up to 70 lb. The Small box is $13.65 at the Post Office ($12.10 online). The Medium box is $24.80 ($21.17 online). The Large box is $34.00 ($31.00 online). A Flat Rate Envelope is $12.90.
Priority Mail and Express Flat Rate prices
| Packaging | Post Office | Online |
|---|---|---|
| Flat Rate Envelope12½" × 9½" | $12.90 | $11.12 |
| Legal Flat Rate Envelope15" × 9½" | $13.25 | $11.66 |
| Padded Flat Rate Envelope12½" × 9½" | $14.00 | $11.99 |
| Small Flat Rate Box8⅝" × 5⅜" × 1⅝" inside | $13.65 | $12.10 |
| Medium Flat Rate Box11" × 8½" × 5½" or 13⅝" × 11⅞" × 3⅜" inside | $24.80 | $21.17 |
| Large Flat Rate Box12" × 11¾" × 5½" inside | $34.00 | $31.00 |
| Express Flat Rate Envelope12½" × 9½" | $35.90 | $31.11 |
| Express Legal Flat Rate Envelope15" × 9½" | $36.20 | $31.43 |
| Express Padded Flat Rate Envelope12½" × 9½" | $36.90 | $31.70 |
Domestic prices effective July 12, 2026, from USPS Notice 123. You must use the USPS-marked Flat Rate packaging.
When it beats zone pricing
- 20 lb in a Medium box (11 × 8½ × 5½ in), zone 8: Ground Advantage $69.40, Priority Mail $109.40. The Medium Flat Rate Box is $24.80 to any zone.
- 2 lb in the same box, zone 2: Ground Advantage $11.50. That is below every Flat Rate box, so the zone price wins.
Limits
- Weight limit is 70 lb. If it does not fit with the box closed, it is not Flat Rate.
- Flat Rate ignores zones and dimensional weight. Your own box is priced by weight, size, and zone.
- These are domestic retail and commercial estimates. The label price is the charge.
Use the calculator
Large empty boxes: how USPS dimensional weight works. Postage steps: how to calculate USPS postage. Compare a box in the USPS shipping calculator.