Counter price from the USPS file; every challenger figure from a purchasable quote dated 2026-07-27.
$24.80 flat versus what we quoted live, 2026-07-27
Five matchups. In each, the medium box's counter fare of $24.80 faces the best live rate our calculator produced that day for a comparable load, checkout totals with SMKlog's portion included. The verdict column keeps score honestly, both directions.
| Load | Lane | Best live rate | Verdict vs $24.80 |
|---|---|---|---|
| 5 lb, 14 × 12 × 6 in | Newark 07102 → Atlanta 30303 | $14.31 FedEx Ground Economy | weight-based, easily |
| 10 lb, 16 × 12 × 10 in | Newark 07102 → Atlanta 30303 | $17.56 UPS Ground Saver | weight-based |
| 10 lb, 16 × 12 × 10 in | Los Angeles 90011 → New York 10001 | $25.51 UPS Ground Saver | near a draw |
| 5 lb at Priority pace | Los Angeles 90011 → New York 10001 | $32.26 USPS Priority Mail | flat box, clearly |
| 20 lb, 18 × 14 × 12 in | Los Angeles 90011 → New York 10001 | $35.06 UPS Ground Saver | flat box, if it closes |
Notice what actually flips the verdict. It isn't weight alone: 10 lb lost to the flat box on one coast and beat it from the other. The winning conditions stack, dense contents, a long haul, and a shape the box can swallow. The fourth row is the sleeper: since flat rate travels on the Priority network, anyone already paying $32.26 for coast-to-coast Priority speed gets the same tier cheaper by squeezing into the fixed-price carton. Buy the postage online rather than at the window and the commercial figure of $21.17 widens every win further.
Two shapes, one decision
The top-loader (11-1/4 × 8-3/4 × 6 in outside, per usps.com, checked 2026-07-27) is the volume play; the side-loader (14 × 12 × 3-1/2) trades depth for footprint. Measure your item against both before concluding it doesn't fit the program.
It moves at Priority speed
Flat rate isn't a slower class of mail, it's Priority Mail with different arithmetic. Our timing captures put that network at 2-3 business days coast to coast and 4-5 on the Newark to Atlanta lane, and the fixed-price box inherits whichever window your lane draws.
The flaps are the contract
Fixed pricing holds only while the box closes on its natural creases. Overstuff it into a bulge and the counter can reprice the whole shipment, which erases the very savings you chose it for. When contents fight the lid, move up a size or switch to weight-based.
Medium flat rate box questions
What are the medium flat rate box dimensions?
Two shapes exist, per usps.com, checked 2026-07-27: a top-loading box at 11-1/4 x 8-3/4 x 6 inches outside and a side-loading one at 14 x 12 x 3-1/2. Same price either way, so pick whichever geometry hugs your item.
How much does the medium flat rate box cost to ship?
$24.80 at the counter or $21.17 with commercial online pricing, per USPS Notice 123, retrieved 2026-07-27, to any US address at up to 70 lb. USPS supplies the empty box without charge.
When should I skip the medium box?
Whenever the load is light or the haul is short. Our 2026-07-27 quotes moved 5 lb from Newark to Atlanta for $14.31 and 10 lb for $17.56, both comfortably under the flat figure. The box earns its keep on heavy, dense, cross-country shipments.
What fits inside a medium flat rate box?
The top-loader swallows a pair of boots, a stand mixer bowl, stacked jeans or a dozen paperbacks; the side-loader suits framed photos, laptops in sleeves and flat parts. For books alone, compare Media Mail first, which carried 5 lb for $7.34 per Notice 123, retrieved 2026-07-27.