Technical Drawing Paper Sizes, Title Block and Scale

Technical drawing is the common language of manufacturing. A designer in one country, a machinist in another and an inspector in a third all understand the same sheet of paper the same way — because everything on it follows agreed rules. Learning those rules is what this course is about.

Before you draw a single line you have to settle three things: which sheet size you will use, where the frame and the title block go on it, and at what scale the part will be drawn. This first lesson covers exactly those three.

What is a technical drawing?

A technical drawing is not a picture of a part — it is a complete manufacturing instruction. A photograph shows you what something looks like; a technical drawing tells you how big it is, how accurate it must be, how smooth its surfaces have to be and what it is made of. Nothing on it is decorative and nothing is left to interpretation.

It is drawn to standards (ISO, EN, TS) so that everyone reads it identically.
It is unambiguous — a drawing that can be read two ways is a faulty drawing.
It is complete — every dimension needed to make the part is written on it.
It is measurable — every requirement on it can be checked with an instrument.

Drawing sheet sizes: the A series

Drawing paper sizes are standardised in the A series (ISO 216 / TS 506). The whole system is built on one sheet: A0, which measures 1189 × 841 mm and has an area of exactly one square metre. Its sides are in the ratio 1 : √2.

Every smaller size comes from halving the longer side of the size above it. Halve A0 and you get two A1 sheets; halve A1 and you get A2, and so on. Because of the √2 ratio, the proportions stay the same at every step — which is why a drawing can be photocopied from A3 to A4 without distortion.

Figure 1.1 — Dividing an A0 sheet to obtain A1, A2, A3, A4 and A5

Size	Dimensions (mm)	Relation
A0	1189 × 841	Base sheet, area 1 m²
A1	841 × 594	Half of A0
A2	594 × 420	Half of A1
A3	420 × 297	Half of A2
A4	297 × 210	Half of A3
A5	210 × 148	Half of A4

How to remember it. You only need one number: A4 is 297 × 210 mm. Double the short side and you have A3 (420 × 297). Double again for A2, and so on. Every step up doubles the area.

Frame and margins

Nothing is drawn right up to the edge of the sheet. A frame is drawn inside the paper edge and all drawing work stays inside it. The margins are not arbitrary:

On A4 the frame is 5 mm from the top, bottom and right edges.
On A3 and larger it is 10 mm from those edges.
The left margin is always 20 mm, on every size — this is the filing edge, where the sheet is punched or bound.
The frame is drawn with a continuous line about 0,5 mm thick.

Figure 1.2 — Frame, margins and title block width on A4 and A3 sheets

The title block

The title block is the identity card of the drawing. It always sits in the bottom right corner, touching the frame, so that it is visible when the sheet is folded to A4. Its width is 185 mm on A4 and 180 mm on A3 and larger.

Figure 1.3 — The title block used in schools — field sizes and the information entered

An industrial title block carries at least: the part name, the drawing number, the material, the quantity, the scale, the projection method (first angle or third angle), who drew it, who checked it, and the date. A school title block is a simplified version of the same thing.

Read the title block first. The scale and the projection method live there. If you start reading views before you know whether the drawing is first angle or third angle, you can end up building a mirror image of the part.

Scale

Real parts are rarely the size of a sheet of paper. Scale is the ratio between the size drawn and the real size:

Scale = drawn size ÷ actual size

1 : 1 — full size. What you see is what the part measures.
2 : 1, 5 : 1, 10 : 1 — enlargement, used for small parts.
1 : 2, 1 : 5, 1 : 10 — reduction, used for large parts.

Figure 1.4 — The same part drawn at 1:1, 2:1 and 1:2 — the dimension figure never changes

The single most important rule about scale: the scale changes how big the drawing looks, but it never changes the dimension figures. A 30 mm feature is written “30” whether the sheet is 1:1, 2:1 or 1:2. Never measure a drawing with a ruler — read the written dimension. If a dimension is missing, ask; do not calculate it from the paper.

Standard scales are chosen from the series in ISO 5455 (TS 3532). Arbitrary values such as 1:3 or 1:7 are not used.

Test yourself

What are the dimensions of A3?
420 × 297 mm — twice an A4 sheet.
Why is the left margin always 20 mm?
It is the filing edge. The sheet is punched or bound there, so no drawing content may fall in that strip.
A drawing is at 1:2 and a shaft is dimensioned “40”. How long is the real shaft?
40 mm. The dimension figure is always the real size; only the drawn length is halved.
Where is the title block and why there?
Bottom right corner. When a large sheet is folded down to A4 the title block stays on the outside and remains readable.
Which sheet has an area of exactly 1 m²?
A0, 1189 × 841 mm.
Can you scale a dimension off the paper with a ruler?
No. Printing, copying and paper stretch all change the drawn size. Only written dimensions are valid.

Next lesson. Now that the sheet is set up, we start drawing on it. Lesson 2 covers the line types used in technical drawing — which line means what, how thick each one is, and the lettering standard.