Postcard size is the most under-thought variable in a print order. Designers default to the size their template ships with; printers default to whatever runs cheapest on their press. Neither of those defaults is wrong — but if you're sending direct mail at scale, the size you pick changes the USPS price tier you fall into, and that's a real number.
The standard postcard sizes
Three sizes cover most jobs. Pick the smallest one that fits your message because postage scales with dimensions and the recipient's attention does not.
4×6
The First-Class Mail postcard size — and the only size USPS prices at the dedicated "postcard" rate. Same form factor as a photo print, so it reads as familiar in a stack of mail. Sweet spot for direct mail where unit economics matter.
5×7
Larger image area, more typographic room, friendly for wedding save-the-dates and event invitations. USPS prices 5×7 as a "letter" not a "postcard" — there's a postage step up. Worth it when the card is meant to be kept on a fridge for months.
6×9
The largest size USPS still rates as a "letter" before jumping to "flat" pricing — useful when you want the impact of a bigger card without the next-tier postage. Common for B2B and real estate because there's enough room for a property photo + body copy + CTA.
EDDM specifics
Every Door Direct Mail has its own size constraints. The eligible sizes are 6.5×9, 6.25×11, 6.5×11, 6.25×12, and 8.5×11 — none of which match the "standard" postcard sizes above. If you're running EDDM, the size question is short: pick the smallest EDDM-eligible size that fits your message, because postage is identical across eligible sizes and bigger cards mean bigger print bills.
Bleed, safe zone, and the dimensions you actually upload
Every postcard size in our catalog assumes 0.125" bleed on each edge and a 0.125" safe zone inside the trim. That means for a 4×6 postcard:
- Final trim: 4 × 6 inches
- Upload size with bleed: 4.25 × 6.25 inches
- Keep important content inside: 3.75 × 5.75 inches
Same math for every size. Tools like Canva and Photoshop have built-in bleed support; check it before you export. The single biggest reason a printer rejects a file is content too close to the trim line.
Orientation
Two notes that get overlooked:
- For direct mail, the USPS expects the address block on the back in a specific orientation. Land your design on the address-aware template version; the post office is not flexible about this.
- Vertical postcards stand out in a horizontal-mail stack. If your recipient sorts mail by skimming, vertical is the cheap trick to win the half-second of attention.
What size should you pick?
- Mailing 5,000+ pieces and watching unit cost → 4×6 First-Class.
- Mailing to a neighbourhood → 6.5×9 EDDM.
- Sending a save-the-date that goes on a fridge → 5×7.
- Real estate or B2B with a hero image → 6×9.
- One-off premium handout → 6×11 or 8.5×11; size becomes the gimmick.