Two measuring systems, two naming conventions that use the same letters for different things, and a set of trade sizes that exist because of press sheets rather than aesthetics. This is the reference we use daily — sheet sizes, cards, invitations, envelopes and the rest of the stationery family, with the traps named.
Three things to know before any table
1. "A7" means two different things. In the United States an A7 is a 5 × 7 inch card — the standard wedding invitation. Under ISO, A7 is 74 × 105 mm, about the size of a luggage tag. The US announcement sizes borrowed the letters and ignored the system. When you brief a printer, say the dimensions.
2. Trade sizes come from press sheets, not taste. A 3.5 × 2 inch business card exists because it lands a clean multiple on a 12 × 18 or 19 × 25 sheet. Ask for 3.6 × 2.1 and you pay for the same sheet with fewer cards on it. Standard sizes aren't a limit on creativity — they're where the price is.
3. ISO A halves cleanly; US sizes don't. Fold any A size in half and you get the next one down at the same 1:√2 proportion. Fold US Letter in half and you get 5.5 × 8.5, a different shape entirely. This is why European stationery families nest and American ones need their own chart.
Fig. 1 — The ISO A series. A0 is exactly one square metre; every size below is the one above folded in half.
Every size on this site is a trim size — the finished piece after cutting. Artwork has to be bigger than that, and the important content has to be smaller.
Fig. 2 — Trim, bleed and safety. Three numbers that prevent most artwork rejections.
Converting units
Unit conversions for print: length, caliper, type size, paper weight and resolution
Quantity
Imperial
Metric
Conversion
Length
1 in
25.4 mm
mm = in × 25.4
Caliper (thickness)
1 pt = 0.001 in
0.0254 mm
16 pt ≈ 0.41 mm · 32 pt ≈ 0.81 mm
Type size
1 pt = 1/72 in
0.353 mm
⚠ a type point ≠ a caliper point
Weight, text stock
80 lb text
≈ 118 gsm
basis 25 × 38 in / 500 sheets
Weight, cover stock
100 lb cover
≈ 270 gsm
basis 20 × 26 in / 500 sheets
Weight, bond/writing
24 lb bond
≈ 90 gsm
basis 17 × 22 in / 500 sheets
Resolution
300 dpi
118 px/cm
press artwork minimum
The point trap. "12 pt" on a stock spec means 0.012 inch thick. "12 pt" on a type spec means a sixth of an inch tall. Same abbreviation, unrelated quantities — and gsm doesn't map cleanly onto either, because it measures mass per area, not thickness. A bulky uncoated 300 gsm cotton and a dense coated 300 gsm sheet can differ by 30% in caliper.