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ANSI Paper Sizes
ANSI/ASME Y14.1 Standard and the ANSI Series
The ANSI/ASME Y14.1 standard defines the ANSI series, the paper size system used in the United States and Canada. While most of the world relies on the ISO 216 standard, the ANSI series remains the dominant system in North America for technical drawings, office documents, and engineering work.
Main Characteristic
The ANSI series is anchored to the familiar Letter size (ANSI A, 8.5 × 11 in), which has been in use in the United States since the early twentieth century and was formally adopted as a government standard in the 1980s. Unlike the ISO A series — which maintains a single consistent aspect ratio of 1:√2 across all sizes — the ANSI series alternates between two aspect ratios: 1:1.2941 (for sizes A, C, and E) and 1:1.5455 (for sizes B and D). As a practical consequence, scaling a document between ANSI sizes does not preserve its layout as cleanly as scaling between ISO sizes; extra margins will appear on the enlarged or reduced sheet.
The Measurement System
Starting Point: The series is based on ANSI A (Letter), measuring 8.5 × 11 in (216 × 279 mm), the most widely used paper format in North America.
Scaling: Each subsequent size is derived by doubling the preceding one along its longer dimension: ANSI B is twice ANSI A, ANSI C is twice ANSI B, and so on. Halving a sheet produces two sheets of the next smaller size, similar in principle to the ISO series.
Common Usage: ANSI A (Letter) is the everyday standard for correspondence and office printing. ANSI B — also known as Ledger (landscape) or Tabloid (portrait) at 11 × 17 in — is widely used for spreads, technical drawings, and newspaper formats.