Practical guide · dimensions explained
A, B, C, Letter and ARCH: find the right paper family
Identify nominal paper dimensions before calculating pixels, especially when similar names describe different standards.
Reviewed September 28, 2026 · Worked examples calculated for this guide
Illustration of the related tool’s example; proportions only.
Begin with the exact format name
A4 and US Letter are common office choices, but they do not share dimensions. A4 is 210 × 297 mm; Letter is 8.5 × 11 inches. A preset makes those units explicit. Use the orientation switch after choosing the format, and verify the finished width and height before entering any bleed or safe-area requirements.
Keep ISO B separate from JIS B
Our B-series table uses ISO dimensions. ISO B5 is 176 × 250 mm. A printer menu or a paper package labeled JIS B5 refers to another family; the name B5 alone is not enough to choose a size. The table’s family filter helps keep these labels visible, but the actual supplier’s dimensions remain the relevant input for a specific product.
A sheet, an envelope and a drawing are different objects
C-series entries are nominal envelope dimensions. C4 is 229 × 324 mm, while A4 is 210 × 297 mm. The envelope’s seams and construction affect its usable interior. ANSI A shares Letter’s dimensions and ANSI B shares Tabloid’s dimensions, so those names are combined in one row. Architectural sizes use separate inch dimensions: ARCH D is 24 × 36 inches.
Calculate from the defining units
Consider A2, defined as 420 × 594 mm. At 300 PPI, nearest whole-pixel rounding gives 4961 × 7016 px. For an ARCH D sheet at the same density, 24 × 36 inches gives exactly 7200 × 10800 px. The reference displays converted units for convenience, but always calculates pixels from the original millimeters or inches. This avoids feeding rounded display values back into the calculation.
Reference notes
References checked September 28, 2026. Calculations and worked examples are our own.