Technical Drawing Standards: Lettering Heights
The BS Standards defines a range of eight Nominal heights for lettering.
The sizes are:
1.8, 2.5, 3.5, 5.0,7.0,10,14 and 20mm
A formula of 1:√2 (≈ 1:1.4) is used to calculate the sizes available,the same formula that calculates paper sizes and line weights.
The recommended Minimum sizes are:
| Paper size | Notes & Dims | Titles | Headings |
| A0 | 3.5 | 5 | 7 |
| A1 | 2.5 | 3.5 | 5 |
| A2 | 2.5 | 3.5 | 5 |
| A3 | 2.5 | 3.5 | 5 |
| A4 | 1.8 | 2.5 | 3.5 |
BS EN ISO 3098-0:1998 Technical product documentation. Lettering. General requirements.