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The standard postcard size in the US is 4 x 6 inches. This is the most cost-effective format because it qualifies for First-Class Mail postcard pricing, which is lower than First-Class Mail letter pricing. Postcards range in size from a USPS minimum of 3.5 x 5 inches to a maximum of 6.125 x 11.5 inches before they are reclassified as flats and charged at a higher postage rate. Every size within that range has different postage costs, print production specs, and design constraints.
TLDR: The 4 x 6 inch postcard qualifies for the lowest USPS postage rate. The 5 x 7 inch and 6 x 9 inch sizes are letter-rate pieces, not postcard-rate, and cost more to mail. Any piece above 6.125 x 11.5 inches or above 4.25 x 6 inches in thickness over 0.016 inches is classified as a flat and charged accordingly.
The most common postcard ordering mistake is choosing a size based on design preference without checking USPS classification. A 5 x 7 inch piece is not a postcard by USPS definition. It is a letter-size mailpiece that costs significantly more to send. For direct mail campaigns where postage is a budget line item, the size decision must be made against the USPS rate table, not against the print catalog.
USPS classifies mailpieces by physical dimensions into three categories: postcards, letters, and flats. Each category carries a different postage rate. The classification is based on the finished piece dimensions, not on what the sender calls the piece. A piece labeled “postcard” that measures 5 x 7 inches is classified and charged as a letter by USPS regardless of the label.
| USPS Classification | Minimum Size | Maximum Size | Thickness Range | 2026 First-Class Rate |
|---|---|---|---|---|
| Postcard | 3.5 x 5 in | 4.25 x 6 in | 0.007–0.016 in | $0.56 (standard retail) |
| Letter | 3.5 x 5 in | 6.125 x 11.5 in | 0.007–0.25 in | $0.73 (standard retail) |
| Flat (large envelope) | 6.125 x 11.5 in (any dimension exceeds letter max) | 12 x 15 in | 0.007–0.75 in | $1.50+ (standard retail) |
USPS requires all letter-size and postcard-size mailpieces to have an aspect ratio between 1.3 and 2.5 (length divided by height). A piece with an aspect ratio outside this range is classified as non-machinable and charged a non-machinable surcharge of $0.40 per piece on top of the standard rate. A square postcard at 5 x 5 inches has an aspect ratio of 1.0, which falls outside the machinable range and incurs the surcharge.
The table below covers every standard postcard size in commercial use, with USPS classification, pixel dimensions at 300 DPI, and canvas size with bleed included on all four sides.
| Size | Size (mm) | Canvas with Bleed | Pixels at 300 DPI | USPS Class | Common Use |
|---|---|---|---|---|---|
| 3.5 x 5 in | 89 x 127 mm | 3.75 x 5.25 in | 1125 x 1575 px | Postcard rate | Minimum machinable size; coupons, small promo |
| 4 x 6 in | 102 x 152 mm | 4.25 x 6.25 in | 1275 x 1875 px | Postcard rate | Standard direct mail, event invitations, retail |
| 4.25 x 6 in | 108 x 152 mm | 4.5 x 6.25 in | 1350 x 1875 px | Postcard rate (maximum) | Maximum postcard-rate size; maximizes design area at lowest postage |
| 4.25 x 5.5 in | 108 x 140 mm | 4.5 x 5.75 in | 1350 x 1725 px | Postcard rate | Quarter-sheet format; dual-use as flyer and mailer |
| 5 x 7 in | 127 x 178 mm | 5.25 x 7.25 in | 1575 x 2175 px | Letter rate | Event invitations, premium direct mail, announcements |
| 5.5 x 8.5 in | 140 x 216 mm | 5.75 x 8.75 in | 1725 x 2625 px | Letter rate | Half-sheet mailer, real estate, service business |
| 6 x 9 in | 152 x 229 mm | 6.25 x 9.25 in | 1875 x 2775 px | Letter rate | High-impact direct mail, restaurant, retail campaign |
| 6 x 11 in | 152 x 279 mm | 6.25 x 11.25 in | 1875 x 3375 px | Letter rate | Jumbo mailer; maximum letter-rate size with high visual impact |
The address side of a postcard that will be mailed through USPS must comply with specific layout requirements. Failure to meet these requirements can result in the piece being returned to the sender, delayed, or assessed a non-machinable surcharge. The requirements apply to both meter-applied and stamp postage.
USPS optical character recognition (OCR) equipment reads the address and prints a barcode in the bottom right area of the mailpiece. The barcode clear zone is the bottom 0.625 inches of the address side, spanning the full width of the piece. No design element, image, text, or color field darker than 20% gray may appear in this zone. Dark backgrounds, dark ink, and dark images in the barcode zone cause OCR read failures and route the piece to manual processing, which delays delivery and can disqualify bulk mail from automation pricing.
The address block itself must sit in the lower right quadrant of the address side, between 0.625 inches from the bottom edge and 2.75 inches from the bottom edge, and between 0.5 inches from the right edge and the center of the piece. Text in the address block must be printed in dark ink on a light background with a minimum type size of 8pt.
The return address must appear in the upper left quadrant of the address side. It must not extend below the horizontal midpoint of the card or into the right half of the address side. Return address type should be 8pt minimum in a legible typeface. Script and display typefaces in the return address block create read-failure risk on automated sorting equipment.
The postage indicia (metered or printed permit imprint) must appear in the upper right quadrant of the address side, within 0.5 inches of the top edge and within 0.5 inches of the right edge. Stamp placement follows the same position. Postage placed anywhere else on the piece is not recognized by processing equipment and the piece is returned.
A postcard built to the correct physical dimensions will still fail in production or in mailing if the file is not set up to the correct technical specifications. These are the four variables that require explicit setup before artwork is built.
Set bleed at 0.125 inches on all four sides of the trim size. Background color, imagery, and design elements that reach the card edge must extend into the bleed area or white paper edges will appear after cutting. The canvas with bleed for a standard 4 x 6 inch postcard is 4.25 x 6.25 inches.
Keep all critical content, including text, logos, and contact information, at least 0.125 inches inside the trim line on the front side. On the address side, keep all design elements at least 0.125 inches inside the trim line on three sides, and at least 0.75 inches from the bottom edge to clear the USPS barcode zone with margin.
Set postcard artwork at 300 DPI at the final print size. A 4 x 6 inch postcard at 300 DPI requires a canvas of 1275 x 1875 pixels with bleed included. Color mode must be CMYK before building the file. RGB files submitted for print are converted by the printer’s RIP software, and that conversion shifts brand-critical colors unpredictably. Set CMYK values for all brand colors before building artwork, not after.
USPS requires postcard-rate pieces to be between 0.007 and 0.016 inches thick. Standard postcard stock runs at 12–16 pt, which converts to 0.012–0.016 inches. This places standard postcard stock within the USPS compliance range for postcard-rate mailing.
Adding laminate film to a postcard adds 0.001–0.002 inches per face. A 14 pt card with double-sided laminate reaches approximately 0.018 inches total thickness, which exceeds the 0.016-inch maximum for postcard-rate classification and reclassifies the piece as a letter. For laminated postcards mailed at postcard rate, use 12 pt stock (0.012 in) to keep the laminated total within the 0.016-inch ceiling.
Stock and finish choices on postcards affect durability in transit, perceived quality on receipt, and mailing compliance. Each variable interacts with the others and must be selected together, not independently.
Uncoated postcard stock accepts ballpoint pen writing cleanly, which is the correct choice for postcards that recipients are expected to fill out and return. Uncoated stock absorbs ink more deeply than coated stock, which reduces color saturation and makes photographic imagery appear flat. For promotional postcards where color accuracy and image sharpness are priorities, coated stock is the correct choice.
Coated stock (gloss or matte) holds ink on the surface, producing higher saturation and sharper edge definition. It does not accept pen writing cleanly. A coated postcard used as a response device (tear-off reply, fill-in coupon) requires an uncoated panel or an uncoated strip, which adds production complexity and cost.
UV spot coating on postcards must not appear in the address zone. A UV-coated surface in the barcode area reflects the USPS barcode printing inkjet unevenly, causing barcode adhesion failure and OCR read errors. Apply UV spot coating to the front face only, or to the back face in areas above the barcode zone, and confirm the coating boundary with the printer before production.
Gloss laminate on the address side creates the same barcode adhesion problem as UV coating. For mailed postcards with full-surface lamination, request matte laminate on the address side and gloss or UV laminate on the front face only. This is a common specification in direct mail production and most printers accommodate it without custom tooling.
The correct postcard size is not purely a design decision. It is a function of the mailing budget, the content volume, the printing quantity, and whether the piece will be mailed or hand-distributed. The table below maps size to use case with the key decision variable for each.
| Size | USPS Rate | Best For | Key Decision Variable | Postage Cost per 1,000 pieces |
|---|---|---|---|---|
| 4 x 6 in | Postcard ($0.56) | High-volume direct mail, coupons | Lowest postage cost per piece | $560 retail / $178–$280 EDDM |
| 4.25 x 6 in | Postcard ($0.56) | Maximum design area at postcard rate | Same postage as 4×6, more design space | $560 retail / $178–$280 EDDM |
| 5 x 7 in | Letter ($0.73) | Premium invitations, announcements | Higher postage; justified by premium positioning | $730 retail |
| 6 x 9 in | Letter ($0.73) | Restaurant, retail, real estate campaigns | High visual impact; stands out in mailbox | $730 retail |
| 6 x 11 in | Letter ($0.73) | High-impact campaigns, luxury brands | Maximum letter-rate size; cannot be folded in standard mailbox | $730 retail |
USPS Every Door Direct Mail allows businesses to mail to every address on a carrier route without a mailing list. EDDM postage rates are significantly lower than standard First-Class retail: approximately $0.178–$0.228 per piece depending on permit type and volume. EDDM pieces must meet specific size requirements that differ from standard postcard and letter sizes.
EDDM pieces must be larger than a standard letter: the minimum EDDM size is 6.125 x 11 inches, and pieces must not exceed 15 x 12 inches. This means standard 4 x 6 and 6 x 9 postcards do not qualify for EDDM pricing. Brands that want EDDM pricing must use a larger format piece, typically 6.5 x 9 inches or 8.5 x 11 inches, which sacrifices some postage savings against the increased print cost for the larger format.
International postcard dimensions follow postal authority standards in each country. A piece mailed from the US to an international address must meet USPS international mail size standards as well as the destination country’s postal acceptance standards. The most common international formats are based on the ISO standard, which uses metric dimensions.
| Country / Standard | Standard Size (mm) | Size (in) | Closest US Size | Notes |
|---|---|---|---|---|
| ISO / Europe standard | 105 x 148 mm | 4.13 x 5.83 in | 4 x 6 in (close) | A6 format; most common in Europe and Asia |
| UK | 152 x 102 mm | 6 x 4 in | 4 x 6 in (landscape) | Same dimensions as US 4×6, landscape orientation default |
| Japan | 100 x 148 mm | 3.94 x 5.83 in | 4 x 6 in (slightly narrower) | Japan Post standard; 5 mm narrower than A6 |
| Australia | 105 x 148 mm | 4.13 x 5.83 in | 4 x 6 in (close) | Follows A6 standard |
| Universal Postal Union (UPU) | 100 x 148 mm minimum / 105 x 148 mm standard | 3.94 x 5.83 in min | 3.5 x 5 in (close to min) | International standard for cross-border postcard mail |
A postcard produced with correct dimensions but an incorrectly set up file will either fail in production or fail at the post office. These are the five file setup steps that must be completed before submitting artwork to a printer for mailed postcard production.
Build the front face at the trim size plus 0.125 inches bleed on all four sides. Set color mode to CMYK. Set resolution to 300 DPI at the canvas size with bleed. Convert all fonts to outlines. Expand all strokes to filled shapes. Embed all placed images. Export as a print-ready PDF with crop marks and bleed marks visible. For high-volume postcard runs, commercial print production from a press-ready PDF eliminates the artwork correction round that slows single-file digital submissions.
Build the address side at the same canvas size as the front face. Reserve the upper right quadrant for postage. Reserve the upper left quadrant for the return address. Keep the lower 0.75 inches of the full card width clear of any design element darker than 20% gray. This provides the USPS barcode zone plus a 0.125-inch margin above the zone boundary. Place the recipient address block in the lower right quadrant, between 0.75 and 2.75 inches from the bottom edge.
If the piece will use a printed permit imprint instead of metered postage, the imprint area must be 1.625 x 1.375 inches in the upper right corner. Confirm the imprint format with USPS or your mail house before building the file.
MFG Merch produces postcards, promotional print, and branded marketing materials for businesses in Jacksonville and nationally. View available print formats in the MFG Merch promotional materials catalog. For orders combining postcards with branded apparel, event merchandise, or trade show materials, consolidated production reduces per-order turnaround time.
Submit artwork at the correct canvas size with bleed, in CMYK at 300 DPI, with the address-side layout meeting USPS zone requirements, and production moves directly to press. Files that do not meet these specifications require a correction round that adds 1–2 business days before printing begins.
USPS postage rates, mailing classifications, and paper stock availability can change over time. The sizes, rates, and specifications in this guide reflect current industry standards and serve as reliable reference points for campaign planning. Before finalizing a mailed postcard campaign, it’s recommended to verify current USPS rates, mailing requirements, and available stock options.
Contact the MFG Merch team for the latest postcard specifications based on available stock weights, current USPS classifications, and your preferred mailing method. Simply provide your postcard size, quantity, mailing method (First-Class, EDDM, or hand distribution), and finish requirements, and our team will send confirmed specifications along with a custom quote.
The standard postcard size in the US is 4 x 6 inches. This size qualifies for USPS First-Class postcard pricing, which is lower than First-Class letter pricing, and fits all standard mailboxes without folding. The maximum size that still qualifies for postcard-rate mailing is 4.25 x 6 inches. Any piece larger than 4.25 x 6 inches is classified as a letter and charged at the higher letter rate.
A USPS postcard-rate piece costs $0.56 per piece at the standard First-Class retail rate as of 2026. A letter-rate piece costs $0.73 per piece. The difference is $0.17 per piece, which adds up to $170 per 1,000 pieces on a direct mail campaign. Postcard-rate pieces must not exceed 4.25 x 6 inches in size and must be between 0.007 and 0.016 inches thick.
Yes. Laminate film adds 0.001–0.002 inches per face to a postcard’s thickness. A standard 14 pt stock (0.014 in) with double-sided laminate reaches approximately 0.018 inches total, which exceeds the 0.016-inch maximum for postcard-rate classification. Laminated postcards intended for postcard-rate mailing should be produced on 12 pt stock (0.012 in) to keep the total laminated thickness within compliance. UV spot coating on the front face only does not create the same compliance risk because it is localized, not full-surface.
The USPS minimum postcard and letter-size mailpiece is 3.5 x 5 inches with a minimum thickness of 0.007 inches. Pieces smaller than 3.5 x 5 inches are not accepted for mailing through standard USPS channels. The aspect ratio must be between 1.3 and 2.5 (length divided by height) or the piece is assessed a non-machinable surcharge of $0.40 per piece.
No. A 5 x 7 inch piece exceeds the USPS maximum postcard-rate size of 4.25 x 6 inches and is classified as a letter. It mails at the First-Class letter rate of $0.73 per piece rather than the postcard rate of $0.56 per piece. The 5 x 7 size is a letter-rate mailpiece in USPS classification regardless of what the sender calls it or how it is designed.
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