Sign Text Size Calculator: Letter Height for Any Viewing Distance
For partially sighted readers, Department for Transport guidance gives 1 mm of letter height for every 100 mm of viewing distance: 30 mm letters read from 3 m, 50 mm from 5 m. The US ADA Standards give almost the same figures at eye level. HSE's table for workplace warning signs asks for half as much from 6 m.
Work out your letter height
Type a capital H at 100 pt, print it at 100% and measure its height in mm. Divide by 35.28 and multiply by 100.
Nothing you enter is sent anywhere. The ADA measures viewing distance from the sign to the nearest obstruction that stops people getting closer, such as a counter or a barrier.
Which part of the letter? The ADA measures the capital letter I; the DfT and HSE documents don't say. This tool applies all three rules to cap height, the height of a capital letter above the baseline. Lower-case letters are shorter, so if you apply the figures to x-height instead, your text comes out larger.
Minimum letter height by viewing distance
Capital-letter heights, rounded up to the next whole millimetre. The ADA column is for text at eye level, with its baseline 1015 to 1780 mm above the floor. The last column gives the font size needed in Open Sans for the largest of the three figures.
| Viewing distance | DfT (÷100) | ADA, eye level | HSE table | Meets all three | Open Sans size |
|---|---|---|---|---|---|
| 0.75 m | 8 mm | 16 mm | 5 mm | 16 mm | 64 pt |
| 1 m | 10 mm | 16 mm | 9 mm | 16 mm | 64 pt |
| 1.5 m | 15 mm | 16 mm | 9 mm | 16 mm | 64 pt |
| 2 m | 20 mm | 18 mm | 18 mm | 20 mm | 80 pt |
| 3 m | 30 mm | 29 mm | 18 mm | 30 mm | 120 pt |
| 4 m | 40 mm | 39 mm | 30 mm | 40 mm | 159 pt |
| 5 m | 50 mm | 50 mm | 30 mm | 50 mm | 199 pt |
| 6 m | 60 mm | 60 mm | 30 mm | 60 mm | 239 pt |
| 8 m | 80 mm | 81 mm | 40 mm | 81 mm | 322 pt |
| 10 m | 100 mm | 102 mm | 50 mm | 102 mm | 406 pt |
| 15 m | 150 mm | 155 mm | 75 mm | 155 mm | 616 pt |
| 20 m | 200 mm | 207 mm | 100 mm | 207 mm | 822 pt |
HSE's table starts at 501 mm, which is why the 0.75 m row shows 5 mm. Its bands step up rather than rising smoothly: every distance from 1.8 m to 3.6 m gets 18 mm.
Two rules agree; the third asks for half
Side by side, the three published rules fall into two camps. The DfT's 1-in-100 rule, written for partially sighted readers, and the ADA's eye-level table land within 2 mm of each other from 3 m to 10 m. HSE's table asks for 40% less at 3 m and exactly half the DfT figure from 6 m on.
They were written for different jobs. The DfT figure comes from its code of practice for accessible railway stations, where the note under the table says the figures are based on someone eligible for registration as partially sighted. The ADA table is part of US accessibility law. The HSE table comes from its guidance on warning signs at major-hazard (COMAH) sites. If your readers include older people or anyone with sight loss, the DfT and ADA figures are the ones written with them in mind.
Font size in points for a given letter height
A font size sets the height of the type's em square, not of the letters, so the same point size gives different capitals in different typefaces. A 100 pt capital is 25.2 mm tall in Open Sans and 23.2 mm in Source Sans 3. Use the font size in the table or larger.
| Typeface (regular) | 10 mm | 15 mm | 20 mm | 25 mm | 30 mm | 40 mm | 50 mm | 60 mm | 75 mm | 100 mm | Cap height |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Open Sans | 40 | 60 | 80 | 100 | 120 | 159 | 199 | 239 | 298 | 398 | 71.4% |
| Roboto | 40 | 60 | 80 | 100 | 120 | 160 | 200 | 240 | 300 | 399 | 71.1% |
| Lato | 40 | 60 | 80 | 99 | 119 | 159 | 198 | 238 | 297 | 396 | 71.7% |
| Montserrat | 41 | 61 | 81 | 102 | 122 | 162 | 203 | 243 | 304 | 405 | 70.0% |
| Poppins | 41 | 62 | 82 | 102 | 123 | 163 | 204 | 245 | 306 | 407 | 69.7% |
| Noto Sans | 40 | 60 | 80 | 100 | 120 | 159 | 199 | 239 | 298 | 398 | 71.4% |
| Source Sans 3 | 44 | 65 | 87 | 108 | 130 | 173 | 216 | 260 | 324 | 432 | 65.6% |
| Atkinson Hyperlegible | 43 | 64 | 85 | 107 | 128 | 170 | 213 | 255 | 319 | 425 | 66.8% |
| Lexend | 41 | 61 | 81 | 102 | 122 | 162 | 203 | 243 | 304 | 405 | 70.0% |
Cap height is shown as a share of the font size. Using a typeface that isn't listed, such as Arial? Choose "Another typeface" in the calculator and measure it with the printed-H method.
Other things that make a sign readable
- Mixed case, not all capitals. The DfT accessible stations code (K3.a and K3.i) asks for upper and lower case because it is read and recognised more quickly; HSE says not to use all capitals for messages longer than a couple of words.
- A plain sans serif typeface. Both the DfT code and HSE ask for sans serif. The ADA rules out italic, oblique, script and highly decorative letters (703.5.3).
- Contrast. Approved Document M Volume 2, paragraph 0.26, treats surfaces as contrasting visually when their light reflectance values differ by more than 30 points (20 points where lighting is above 200 lux). Inclusive Mobility (DfT, 2021, section 4.1) gives a quick check: photograph the sign in black and white, and good contrast stays black and white while poor contrast turns grey.
- Mounting height. The ADA puts visual characters at least 1015 mm above the floor (703.5.6). The DfT stations code gives a standing eye line of about 1400 to 1700 mm for signs read close up (K1.b).
- Where the law fixes a size. In England, fire-service floor signs in blocks of flats with a top storey over 11 m need sans serif letters at least 50 mm high and floor numbers at least 75 mm, mounted 1.7 to 2 m above the floor (Approved Document B, Volume 1, paragraph 15.14); in high-rise residential buildings (18 m or seven storeys and over) this is a legal duty under the Fire Safety (England) Regulations 2022, regulation 8. From 1 January 2027 the tobacco age-of-sale notice must be at least A3 with characters at least 21 mm high in England (SI 2026/996) and 12 mm in Wales (WSI 2026/124).
- Safety signs. The Health and Safety (Safety Signs and Signals) Regulations 1996 only require signs to be easily seen and understood. HSE's guidance on them (L64) refers to BS 5499-4 and BS 5499-10 for sizes.
Sources and how we calculated
We checked every source below on 29 October 2026. The calculator uses the three that turn a viewing distance into a letter height:
- DfT rule: Design Standards for Accessible Railway Stations: a code of practice, Department for Transport and Transport Scotland, version 04, valid from 20 March 2015, item K3.f: reading distance (mm) ÷ 100 = character height (mm). Guidance.
- ADA rule: 2010 ADA Standards for Accessible Design, section 703.5.5 and Table 703.5.5, US Access Board. US federal law. We use the metric figures printed in the Standards (16, 51 and 75 mm, plus 3.2 mm per 305 mm) and apply the per-foot step pro rata.
- HSE rule: Warning signs, HSE technical measures guidance for COMAH sites (page dated 19 August 2025): the non-VDU table up to 6000 mm, then viewing distance ÷ 200.
Every minimum height is rounded up to the next whole millimetre and every font size up to the next whole point. Typeface measurements are our own: the height of the capital I and the lower-case x, measured from the outlines of the regular weight in the Google Fonts repository files on 29 October 2026 (Open Sans 3.003; Roboto 3.015; Lato 2.015; Montserrat 9.000; Poppins 4.004; Noto Sans 2.015; Source Sans 3 3.052; Atkinson Hyperlegible 1.006; Lexend 1.007).
Approved Document M points readers to BS 8300 and the Sign Design Guide for signage. Both are paid publications, as are the BS 5499 and BS ISO 3864 safety-sign standards, so we haven't reproduced their figures. This is general information, not a compliance certificate.
How to cite
You're welcome to link to the calculator or reuse the tables. Please credit Cherry Grove Craft and link to this page:
Cherry Grove Craft (2026). Sign Text Size Calculator: letter height for viewing distance under DfT, HSE and US ADA rules. Checked 29 October 2026. https://cherrygrovecraft.co.uk/pages/sign-text-size-calculator
Licence: our tables and calculations are free to reuse, including commercially, under the Creative Commons Attribution 4.0 licence (CC BY 4.0). The source documents keep their own licences.
Frequently asked questions
How big should the letters on a sign be?
It depends on how far away people read it. The Department for Transport's accessible stations code gives 1 mm of letter height for every 100 mm of viewing distance, based on partially sighted readers: 30 mm for 3 m and 50 mm for 5 m. The US ADA Standards give almost the same figures at eye level. HSE's warning-sign table asks for 18 mm at 3 m and half the DfT figure from 6 m.
What font size can be read from 3 metres?
Under the DfT rule, capital letters read from 3 m should be 30 mm high. In Open Sans that is a 120 pt font size; HSE's lower figure of 18 mm is 72 pt. The point size needed varies by typeface because each one draws its capitals at a different share of the font size, so use the calculator above for yours.
Is there a UK law on the size of text on a sign?
Not for business signs in general. The Health and Safety (Safety Signs and Signals) Regulations 1996 require safety signs to be easily seen and understood without setting sizes. Two fixed minimums do exist: fire-service floor signs in blocks of flats in England over 11 m need 50 mm letters and 75 mm floor numbers (Approved Document B, paragraph 15.14), and from 1 January 2027 the tobacco age-of-sale notice needs characters at least 21 mm high in England and 12 mm in Wales.
Should the text on a sign be in capital letters?
No. The DfT accessible stations code says to use mixed upper and lower case because it is read and recognised more quickly than capitals only, and HSE's warning-sign guidance says not to use all capitals for messages longer than a couple of words.
What character height do the ADA Standards require?
For visual characters with a baseline 1015 to 1780 mm above the floor, the 2010 ADA Standards require at least 16 mm (5/8 inch) up to a viewing distance of 1830 mm (6 feet), plus 3.2 mm (1/8 inch) for every 305 mm (foot) beyond that. Higher signs start at 51 mm and 75 mm. Height is measured on the capital letter I. These are US rules, not UK law.