Large envelope postage (2026)

Q: What counts as a USPS large envelope (flat)?

In this calculator, a flat is any piece that does not fit letter limits or exceeds 3.5 oz while still meeting retail flat maximums—flexible, uniformly thick, rectangular, within 15 by 12 by 0.75 inches, and not over 13 oz.

Q: Can I mail a 14 oz flat at First-Class retail?

First-Class retail flats top out at 13 ounces on the USPS table used here. Heavier pieces usually need a different service—confirm at USPS.

Q: Does this include metered or Commercial Base pricing?

No. This calculator uses the USPS Notice 123 retail single-piece row for large envelopes (flats). Metered letters and commercial discounts use different tables.

Q: What if the calculator says unsupported instead of a dollar total?

Large-envelope-sized mail that is rigid, uneven, or over retail maximums may be priced as a parcel—not as a First-Class flat. This tool explains that case instead of guessing parcel zones.

How much is a First-Class large envelope in 2026?

For 2026, USPS Notice 123 lists First-Class large envelope (flat) retail prices by ounce—for example $1.63 for the first ounce and tiered totals up to 13 oz. That is separate from letter retail starting at $0.78 for the first ounce. Use the calculator's Large envelope / Flat mode when you are not in letter class.

First-Class large envelopes (flats) use their own retail ounce table—not letter Forever-stamp math. Below you can estimate totals for flexible flats that fit USPS retail maximums, with Letter vs Flat modes when you need control.

Mail class

Auto (from dimensions & weight)LetterLarge envelope / Flat

Weight (oz)

Length (in)

Height (in)

Thickness (in)

Shape & contents

Square envelope (height and length similar)Rigid (cards, stiff mailers)Contains objects (not paper only)

Classification

Large envelope / flat (First-Class Mail)

This is considered a large envelope because longest side exceeds the 11.5 inch letter limit, and shortest side exceeds the 6.125 inch letter limit.

Total postage

$1.90

First ounce (flat retail)$1.63
Additional ounces (flat tier; not letter ladder)$0.27
Letter non-machinable surcharge (not used on flats)$0.00

Stamps to use

Retail flat total is $1.90. Cover it with enough postage (Forever stamps are $0.78 face each toward the total) or buy exact large-envelope postage at USPS.

Notes

Weight rounded up to 2 billable oz (First-Class flat retail table).

Pricing follows USPS Notice 123 retail large-envelope (flat) totals—not letter Forever-stamp ladders.

Rates updated: March 2026 — Based on USPS First-Class Mail retail pricing

Large envelope (flat) totals follow USPS Notice 123 retail First-Class flat pricing—not letter Forever-stamp ounce ladders.

Retail flat totals (single-piece)

The site applies the Notice 123 retail row for flats: 1 oz through 13 oz as published. Letter non-machinable surcharges do not apply to flat pricing the way they do for letters; rigid or uneven pieces are flagged toward parcel-style handling instead.

The flat row is tiered by whole ounces (weight not over 1 oz, 2 oz, and so on)—it is not the same as adding $0.29 per ounce forever like many letter calculations. That is why two billable ounces on a flat might not equal “first ounce + one letter additional ounce” in dollars.

Maximum dimensions in this model: 15″ × 12″ × 0.75″ thick, aligned with common USPS retail flat language; always confirm borderline packaging at retail.

Why flats need their own lane

Catalog envelopes, document mailers, and many 9×12 packets exceed letter length or thickness limits. Once USPS treats the piece as a large envelope, retail pricing follows the flat table—not the letter ounce ladder on 1 oz letter guides.

Letter vs flat in one tool

Set Mail class to Auto for everyday mixed use, or choose Letter when you are sure the piece fits letter limits. Choose Large envelope / Flat when you already know you are mailing a flat and want the Notice 123 estimate without forcing letter rules.

Worked example: 2 oz flat

If the calculator classifies your mail as a flat and weight rounds to 2 billable oz, the total in this tool matches the Notice 123 cell for that tier—for example $1.90 at the 2 oz step on the current table. Compare that to letter retail for 2 oz machinable mail on 2 oz letter postage: same year, different product row.

Common mistakes

Using letter Forever math on flats: stacking one Forever plus additional-ounce stamps from habit can underpay a flat. Ignoring flex rules: a rigid photo mailer can fail flat eligibility even if the length and width look like a catalog envelope. Skipping weight: flats jump tiers when billable ounces increase—re-weigh after you add inserts.

Methodology note

This site's letter and flat amounts are checked against USPS Notice 123 for domestic retail single-piece First-Class Mail. When USPS updates retail prices, we refresh the published rate tables used here so the calculator stays aligned with the same Notice 123 rows.

Related guides

Compare flat envelope postage, manila envelope flats, and stamps for a 9×12 when you need scenario-specific wording. For letter-only ounces, use 2 oz letter postage.

Frequently asked questions

What counts as a USPS large envelope (flat)?

In this calculator, a flat is any piece that does not fit letter limits or exceeds letter weight while still meeting retail flat maximums—flexible, uniformly thick, rectangular, within 15″ × 12″ × 0.75″, and not over 13 oz. Rigid or lumpy mail is modeled as parcel-style (not priced here as a flat).

Is large envelope postage the same as letter Forever stamps?

No. Retail flats use Notice 123 flat totals (for example 1 oz at $1.63), not the letter first-ounce ladder starting at $0.78.

Can I mail a 14 oz flat at First-Class retail?

First-Class retail flats top out at 13 ounces on the USPS table used here. Heavier pieces usually need a different service—confirm at USPS.

Does this include metered or Commercial Base pricing?

No. This calculator uses the USPS Notice 123 retail single-piece row for large envelopes (flats). Metered letters and commercial discounts use different tables.

What if the calculator says unsupported instead of a dollar total?

Large-envelope-sized mail that is rigid, uneven, or over retail maximums may be priced as a parcel—not as a First-Class flat. This tool explains that case instead of guessing parcel zones.

Educational estimate only. Not affiliated with USPS. Confirm rigid/parcel cases at retail.