Anatomy of an engineering drawing: title block, revisions, notes and sheet sizes

Every drawing you release, check or send to a supplier carries the same furniture: a frame, a title block, a revision block, notes and a sheet size. None of it describes the part’s shape. Yet most checker rejections of a new engineer’s drawings start here: a missing approval, a revision that does not match the change note, a general tolerance box left blank.

The sections below walk round the sheet in the order a checker does, showing where everything lives and which standard puts it there. Views, lines and dimensions come in later lessons.

Engineering drawing sheet sizes: ISO A series and ASME inch sheets

ISO drawings use the A series from ISO 216:2007. Each size is half the previous one. Every sheet has the same side ratio, the square root of 2, so an A3 drawing reduces to A4 without distortion. ASME Y14.1-2020 (which consolidated the former inch and metric Y14.1 documents) defines the US inch sheets A to E alongside the metric sizes.

The pairs are rough equivalents, not conversions: a B sheet is shorter and wider than A3. When a supplier prints an inch drawing on metric paper, do not let a PDF viewer “fit to page”. The title block still states the scale of the original sheet.

Sheet layout: frame, filing margin, centring marks and grid zones

ISO 5457:1999 (with Amd 1:2010) sets the layout. The 1999 text shows A0 to A3 used landscape and A4 portrait.

The engineering drawing title block: ISO 7200 fields

ISO 7200:2004 defines the data fields in title blocks and document headers. It fixes which data must be present, not one drawing of the block. Its example block is 180 mm wide, so it fits a folded A4. Eight fields are mandatory.

Scale, the projection symbol, the general tolerance statement and the default surface texture are not ISO 7200 data fields. They are shown when used, in boxes placed alongside the title block. The projection symbol from ISO 5456-2:1996 is covered in Lesson 2. The general tolerance entry (for example ISO 2768-1:1989 class m) and the units box (mm) apply to every dimension that has no tolerance of its own.

Scales come from ISO 5455:1979: full size is 1:1, and enlargements are 2:1, 5:1, 10:1, 20:1, 50:1. Reductions are 1:2, 1:5, 1:10, 1:20 and onwards. The main scale goes in the title block area. Any other scale is written next to the view it applies to.

Revision block and revision letters

The revision index identifies the issue. Each time a released drawing changes, the letter moves on (A, B, C…). A line in the revision block records the letter, a short description or change note reference, the date and the approval. On ISO sheets the revision block often sits above the title block; many US formats put it at the top right. Letters I and O are avoided because they read as 1 and 0. Company procedures often skip further letters and differ on whether the first release is A, 0 or a dash, so follow yours. In the US, ASME Y14.35-2025 governs revision of drawings and product definition datasets.

Two rules matter more than any format. First, the revision in the title block, the revision block and the change record must agree. Second, changed features are usually identified on the sheet (a revision triangle or zone reference), so the reader can find what moved.

Notes, “do not scale” and drawing types

Notes carry the requirements that geometry cannot: material and specification, heat treatment, finish, marking, edge breaks, inspection. General notes apply to the whole drawing and are grouped in one area, often above or to the left of the title block. Local notes sit next to the feature they control, with a leader. Flag notes are written once in the notes list. Each feature calls one up by its number inside a flag symbol, which keeps a crowded view readable.

“Do not scale” (often “DO NOT SCALE DRAWING”) means that nobody may measure the print to find a size. Prints shrink, PDF viewers resize, and views are often drawn out of scale after late changes. The only valid size is the stated dimension with its tolerance; if a dimension is missing, the supplier must ask.

ASME Y14.24-2020 classifies drawing types. The three you meet first:

Drawing type	What it defines	Typical content
Detail	One part, completely	Views, dimensions, tolerances, material, finish
Assembly	How parts go together	Item balloons, parts list, assembly notes, torques
Installation	How an item fits into its next higher assembly or vehicle	Interfaces, envelope, attachment points, installation notes

The parts list on an assembly follows ASME Y14.34-2013 (R2024), which covers associated lists. Each entry gives a find (item) number, quantity, part number and description, linked to a balloon on the views.

Engineering drawing standards: ISO and ASME side by side

A UK drawing office usually works to BS 8888:2025, which calls up the ISO set. A US office works to the ASME Y14 series under ASME Y14.100-2017. Knowing the pairs saves time when a supplier or a customer works to the other system.

With the sheet furniture understood, the next step is the views themselves. Lesson 2 explains first angle and third angle projection and the symbol that sits beside the title block. When your notes reach tolerances, the tolerance stack-up calculator shows how those general tolerances add up across an assembly.