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EDDM Size Checker.

Check whether your mailpiece size and weight qualify for USPS EDDM Retail, and see exactly why if it does not.

EDDM Retail eligibility

This checks USPS EDDM Retail's published dimension, thickness, and weight rules. It does not check design requirements like the required "ECRWSS" or "Postal Customer" indicia, which are separate from size eligibility.

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The Rule Most Postcards Fail

EDDM Retail is a flat-size mailing service, and USPS defines "flat" by a piece exceeding at least one of three thresholds — length over 10.5 inches, height over 6.125 inches, or thickness over 0.25 inches. A mailpiece that fits within all of USPS's letter-size dimensions on every measurement is a letter, not a flat, and does not qualify for EDDM Retail regardless of how well it otherwise fits the general size range.

EDDM Retail Requirements

Length: 3.5″ – 15″
Height: 3.5″ – 12″
Thickness: 0.007″ – 0.75″
Weight: 3.3 oz maximum
Must exceed: length > 10.5″, OR height > 6.125″, OR thickness > 0.25″

This is exactly why a standard 4x6 postcard does not qualify: 4 inches and 6 inches both sit comfortably within the letter-size range on every dimension, so it never exceeds any of the three flat-size thresholds, regardless of its weight or thickness being otherwise fine.

Sizes That Reliably Qualify

6.5″ × 9″

Height of 9″ clears the 6.125″ flat threshold comfortably, a common choice for postcard-style EDDM mailers that still want a compact size.

8.5″ × 11″

Standard letter-paper dimensions, both length and height clearing their respective flat thresholds, and a size print vendors can produce cheaply since it needs no custom trim from standard stock.

8″ × 10″

A middle-ground size between the two above, also comfortably clearing the flat thresholds on both length and height.

Size Is Not the Only Requirement

Passing the size, thickness, and weight checks is necessary but not sufficient on its own. EDDM Retail mailpieces also need the required indicia — either "ECRWSS" (Enhanced Carrier Route Walk Sequence Saturation) or "Postal Customer" printed on the address side, plus a simulated postage indicia showing the permit-style marking rather than an actual stamp. Those are design and printing requirements checked separately from the physical size eligibility this tool covers.

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The distinction between USPS letter-size and flat-size mail exists because the two categories are processed differently in USPS's sorting equipment, and different postage rates apply to each. EDDM Retail is specifically a flat-size product — a mailpiece within letter-size dimensions on every measurement, even if otherwise well within the general 3.5″–15″ length and 3.5″–12″ height range, is processed and priced as a letter instead, and cannot use EDDM Retail rates or its no-permit, no-mailing-list submission process.

Thickness alone can technically satisfy the flat-size threshold at over 0.25 inches, but this is unusual for a typical printed mailpiece — a postcard or flyer thick enough to qualify through thickness alone would be closer to a small booklet or a padded mailer than a standard printed piece, so in practice nearly every EDDM mailpiece qualifies through length or height, not thickness.

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Why does a 6x9 postcard qualify but a 4x6 does not?

A 6x9 piece has a height of 9 inches, which exceeds the 6.125-inch flat-size threshold. A 4x6 piece has a maximum dimension of 6 inches, which clears neither the 10.5-inch length threshold nor the 6.125-inch height threshold, so it is processed as a letter, not a flat, and does not qualify for EDDM Retail.

Does the shape need to be a perfect rectangle?

Yes — EDDM Retail requires a rectangular mailpiece. Die-cut shapes, rounded corners beyond USPS's allowed tolerance, or non-rectangular forms can be disqualified even when the overall length and height measurements would otherwise pass.

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