Counter figures come from the USPS price file; every rival number is a dated production quote from 2026-07-27. No blending between the two.
Current flat rate prices (USPS Notice 123, retrieved 2026-07-27)
These are Priority Mail flat rate products: one price to any state, contents up to 70 lb, delivery on the Priority network. The commercial column is what USPS charges when postage is bought online instead of at the window.
| Product | Size | Counter price | Commercial online |
|---|---|---|---|
| Flat rate envelope | 12-1/2 x 9-1/2 in | $12.90 | $11.12 |
| Legal flat rate envelope | 15 x 9-1/2 in | $13.25 | $11.66 |
| Padded flat rate envelope | 12-1/2 x 9-1/2 in | $14.00 | $11.99 |
| Small flat rate box | 8-5/8 x 5-3/8 x 1-5/8 in | $13.65 | $12.10 |
| Medium flat rate box | 11 x 8-1/2 x 5-1/2 in (or 13-5/8 x 11-7/8 x 3-3/8) | $24.80 | $21.17 |
| Large flat rate box | 12 x 11-3/4 x 5-1/2 in | $34.00 | $31.00 |
| Large flat rate box, APO/FPO/DPO | 12 x 11-3/4 x 5-1/2 in | $32.55 | $29.59 |
When flat rate wins, on real numbers
We put the flat menu against Ground Advantage quotes captured through our checkout on 2026-07-27, using a 25 x 20 x 10 cm carton on Newark to Atlanta and Los Angeles to New York. One caveat printed up front: the flat rate rows travel at Priority speed while these Ground Advantage quotes carried 6-7 day windows, so a flat rate loss on price can still be a win on urgency.
| Contents weight | Route | Ground Advantage | Flat rate option | Flat rate price | Cheaper approach |
|---|---|---|---|---|---|
| 2 lb | Newark → Atlanta | $8.48 | Small box | $13.65 | Weight-based, by a lot |
| 5 lb | Newark → Atlanta | $14.67 | Medium box | $24.80 | Weight-based |
| 15 lb | Newark → Atlanta | $23.69 | Medium box | $24.80 | Weight-based, barely |
| 5 lb | Los Angeles → New York | $20.84 | Medium box | $24.80 | Weight-based |
| 10 lb | Los Angeles → New York | $30.09 | Medium box | $24.80 | Flat rate |
| 15 lb | Los Angeles → New York | $35.33 | Large box | $34.00 | Flat rate |
The pattern holds across the table: short hauls and light contents favor weight-based pricing decisively, $8.48 against $13.65 at 2 lb from Newark. Stack up both weight and distance and the menu flips, $24.80 beating $30.09 for 10 lb across the country. Flat rate is a bet that your parcel is heavy, far-bound and small enough to fit; lose any leg of that bet and the plain carton wins.
Fit is the silent constraint
The medium box tops out around 11 x 8.5 x 5.5 inches. Plenty of 10 lb items are dense enough to justify flat rate but shaped wrong for it, and an item that forces the large box surrenders most of the savings before it leaves the house.
Buy postage online either way
The gap between counter and commercial columns is pure channel pricing for identical handling, $24.80 versus $21.17 on the medium box. Whoever sells you the label, avoid paying window prices for it.
Military addresses get a break
The large box has a dedicated APO/FPO/DPO price of $32.55, under the domestic $34.00. If you ship care packages to service members, that line item exists specifically for you.
Flat rate questions with sourced answers
What do USPS flat rate boxes cost right now?
Per USPS Notice 123, retrieved 2026-07-27: small box $13.65, medium box $24.80, large box $34.00 at the counter, with the flat rate envelope at $12.90. Online commercial pricing runs lower, $12.10, $21.17 and $31.00 for the same three boxes.
Is flat rate cheaper than weight-based shipping?
Usually not for light parcels. Our 2026-07-27 checkout capture priced a 2 lb box from Newark to Atlanta at $8.48 on Ground Advantage, well under the $13.65 small box. Flat rate started winning only when weight and distance piled up together, like 10 lb from Los Angeles to New York at $30.09 against the $24.80 medium.
Does 'if it fits, it ships' ignore weight completely?
Up to 70 lb, yes: the box price is the box price regardless of what's inside, and the parcel travels at Priority Mail speed. That's exactly why dense items headed across the country are the classic flat rate use case.
Can I buy flat rate postage through SMKlog?
Our checkout prices your actual carton by its size, weight and route, which on most light parcels beats the flat menu. The flat rate figures on this page are USPS counter and online prices, listed so you can compare both approaches before paying anywhere.