What is a standard and why do we need it?
A standard (or norm) is a written agreement on how something should be made, measured, tested or described. Experts, makers and users agree it together.
Standards give:
- Fit and interchangeability: screws, plugs, batteries and paper from different makers work together.
- Safety: toys, helmets, electrical goods and furniture are tested the same way.
- Quality: buyers know what they get. ISO 9001 is a standard for quality management.
- Fair trade: one rule across many countries makes exporting easier.
- Clear communication: drawings and symbols mean the same everywhere.
Standardisation is the process of making and using standards. It also cuts costs because fewer different parts are needed.
Who writes standards? National and international bodies
- ISO (International Organization for Standardization) and IEC (for electrical goods) write world standards.
- CEN writes European EN standards.
- National bodies: BIS (India), BSI (UK), DIN (Germany), UNE (Spain), ANSI (USA), JIS (Japan).
A code shows the levels: BS EN ISO 9001 = an ISO standard adopted as a European and then a British standard.
Conformity marks
- CE: the maker declares the product meets EU safety, health and environment law (UKCA is the UK version).
- Kitemark: BSI has tested the product and checks the factory.
- ISI mark: BIS certifies the product meets an Indian Standard; it is compulsory for items like helmets and pressure cookers.
Examples for designers
Toy safety (ISO 8124, EN 71: small parts, sharp edges, flammability, toxic paint); furniture strength; electrical safety; anthropometric data (body sizes) used in ergonomics; and environmental standards such as ISO 14001.
Paper formats: the A series (ISO 216)
A0 has an area of 1 m² and sides 841 × 1189 mm. Each next size is the one before cut in half across its long side.
| Size | mm |
|---|---|
| A0 | 841 × 1189 |
| A1 | 594 × 841 |
| A2 | 420 × 594 |
| A3 | 297 × 420 |
| A4 | 210 × 297 |
| A5 | 148 × 210 |
Why the ratio 1 : √2? If long ÷ short = √2, then after halving, the new long ÷ short is still √2. So the shape never changes, and you can enlarge A4 to A3 (×1.41 per side) or reduce A3 to A4 (×0.71 per side) with no distortion. B and C series fit around A (C4 envelopes hold A4 sheets).
Technical drawing standards and folding
Lines (ISO 128)
- Thick continuous: visible edges and outlines.
- Thin dashed: hidden edges.
- Thin chain (long dash, short dash): centre lines and axes of symmetry.
- Thin continuous: dimension and projection lines, hatching.
Scales (ISO 5455)
Scale = drawing size : real size. Full size 1:1; reduction 1:2, 1:5, 1:10; enlargement 2:1, 5:1.
Dimensions (ISO 129)
All in millimetres, with no unit written; numbers sit above the dimension line; each size is given once.
Title block and projection
Bottom-right corner: title, name, scale, date, sheet size and the projection symbol (first-angle used in Europe and India, third-angle in the USA).
Folding to A4
Large sheets are folded to A4 (210 × 297 mm) so they fit in a file: first fold the long side in zig-zag (accordion) folds, then fold across, always leaving the title block visible on the front.
Try it
Take an A4 sheet and fold it in half: you have A5. Measure it. Divide the long side by the short side for both sheets; both answers should be close to 1.41. Then find three marks (CE, ISI, Kitemark or others) on products at home and write what each means. Use the slider in the last 3D step to check sizes.
Key formulas and definitions
- Area of A0 = 1 m²; area of An = 1 ÷ 2ⁿ m²
- Long side ÷ short side = √2 ≈ 1.414 for every A-size
- A4 = 210 × 297 mm; A3 = 297 × 420 mm
- Scale = drawing length : real length
- Real length = drawing length × scale factor (e.g. ×5 for 1:5)
- Area changes by (linear scale)²
- BS EN ISO = an ISO standard adopted in Europe and the UK
Worked examples
1. What is the area of an A4 sheet in m²?
A4 is A0 halved four times: 1 ÷ 2⁴ = 1 ÷ 16 = 0.0625 m². Check: 0.210 × 0.297 = 0.0624 m².
2. How many A4 sheets can be cut from one A1 sheet?
A1 → A2 (2) → A3 (4) → A4 (8). So 8 sheets of A4.
3. A part is 150 mm long. How long is it on a drawing at scale 1:5?
Drawing length = 150 ÷ 5 = 30 mm.
4. On a 2:1 drawing a slot measures 24 mm. What is its real length?
2:1 means the drawing is twice real size. Real length = 24 ÷ 2 = 12 mm.
5. Show that halving an A3 sheet keeps the same ratio.
A3 = 297 × 420: 420 ÷ 297 = 1.414. Halving the long side gives 297 × 210, which is A4: 297 ÷ 210 = 1.414. Same ratio, same shape.
6. A designer reduces an A3 drawing to fit A4. What percentage should be set on the photocopier?
Each side must be multiplied by 210 ÷ 297 ≈ 0.707, so set about 71%. The area becomes half.
Common mistakes
- Thinking a CE mark means an independent lab tested the product. CE is the maker's own declaration; the Kitemark involves third-party testing.
- Writing "mm" after every dimension on a drawing. Under ISO practice the unit is stated once in the title block.
- Mixing up scales: 1:2 is half size, 2:1 is double size.
- Believing A4 is half of A2. A4 is a quarter of A2; it is half of A3.