Hand-lettered cards are popular for birthdays, weddings and small businesses. Whether you draw by hand or use a design tool, one practical question comes first: will the card actually go through the post? This guide sets out the dimensions and rules from the US Postal Service (USPS) Domestic Mail Manual, then lists what to check before you pay for an online lettering tool. It covers US domestic mail only. For other countries, check your own postal service.

We have not tested any lettering tool, printer or paper named here. Rules and prices change, so check the current versions.

US Postal Service rules for cards and letters

Source: USPS, Domestic Mail Manual 101, "Physical Standards for Machinable Letters, Cards, Flats, and Parcels" (pe.usps.com/text/dmm300/101.htm). Read in a browser. Last checked: 18 October 2026.

Letter-size mail (section 1.1):

  • Minimum: not less than 5 inches long, 3-1/2 inches high and 0.007 inch thick. A piece over 6 inches long or 4-1/4 inches high needs at least 0.009 inch thickness.
  • Maximum: not more than 11-1/2 inches long, 6-1/8 inches high or 1/4 inch thick, and no more than 3.5 ounces.
  • Shape: rectangular, with four square corners and parallel sides. Card stock may have corners rounded to a radius of no more than 0.125 inch.

Cards at card prices (section 6.2.2):

  • Rectangular, not less than 3-1/2 inches high, 5 inches long and 0.007 inch thick.
  • Not more than 4-1/4 inches high, 6 inches long or 0.016 inch thick, and no more than 3.5 ounces.

What makes a letter-size piece nonmachinable (section 1.2) and therefore subject to a surcharge: an aspect ratio (length divided by height) under 1.3 or over 2.5, plastic wrapping or a non-paper exterior, clasps, strings or buttons, uneven thickness from items such as pens or coins, a piece too rigid to bend around the machine, being too thin for its size, or an address parallel to the shorter side.

What this means for a card: a square card has an aspect ratio of 1, below the 1.3 minimum, so a square letter-size card is nonmachinable and the page says such pieces are subject to the surcharge. Rhinestones, buttons and thick embellishments can also cause the uneven-thickness problem. Check the Domestic Mail Manual or ask your local post office before you print a batch. The page is long and has more detail than this summary.

Before you pay for an online lettering tool

  1. Read what it does. One example is Fontilo's Lettering Generator Plus (fontilo.com), described on its page as a design tool for hand lettering, cards, logos and social posts, with fonts, graphics and templates, optional AI graphics and wording, and vector export for plotters.
  2. Check the licence. The page positions the Plus plan for hobby use, the Business plan for professional and educational use, and says reselling designs needs the Reseller plan. If you plan to sell cards, read the terms of use first.
  3. Check the price and period. When we read the page on 18 October 2026 it listed Plus at $60 a year or $5 a month including VAT, with Business and Reseller plans above it. Prices change and may differ in your currency, so confirm at checkout.
  4. Check the refund and cancellation terms. The page says you can return the product within 60 days without stating a reason and can cancel at any time.
  5. Check the file formats. The page lists JPG, PNG and PDF export and a maximum of 6000 x 6000 pixels. Compare that with your printer or print shop: a postcard at 300 dots per inch needs far fewer pixels than that.
  6. Treat speed claims as marketing. "In just a few minutes" depends on your skill and your design.
  7. Know the alternatives. Pen, paper and a scanner cost little and need no subscription. A tool saves time and gives you templates.

Sources: USPS Domestic Mail Manual 101; Fontilo Lettering Generator Plus (details as listed there on 18 October 2026).