## Numbers, units and symbols

If you need to write a minus (negative) number, use a hyphen because some screenreaders do not read out the negative symbol. Do not use a non-breaking hyphen because that is not read as a negative either.

### Numbers

Use numerals (including for 1 to 9). Write numbers out in full if they appear at the start of a sentence, but use numerals if they are at the start of a heading or title.

We spell out 'one' when it means 'a' or to avoid repeating a word. For example, 'never take 2 doses at the same time to make up for a forgotten one'. We also use 'one' in phrases like 'one or the other', 'one of the first', 'one of the most common', 'one at a time'.

Spell out and hyphenate common fractions, such as one‑half.

Spell out first to ninth. Use 10th and so on afterwards.

Avoid long strings of zeros by spelling out millions and billions (£4.2 million not £4,200,000).

Use US billions (1,000 million) not UK billions.

Use a comma for 4‑digit numbers and above (4,000, 10,000).

Be consistent when rounding figures: '4.3 compared with 9.0' not '4.3 compared with 9'. Use a 0 when there's no digit before the decimal point (0.7 not .7).

### Units

Do not put a space around symbols (p<0.01; -12°C; p=0.012).

Use non-breaking spaces between numbers and units (Ctrl+Shift+Space), except for percentages and temperatures (37°C, 76%).

Use the International System of Units (SI units) except for mmHg for blood pressure and other situations in which non-SI units are standard (for example, ml for millilitres). For some audiences you might want to use imperial measurements, for instance to describe weight. In these cases, always include the metric equivalent in brackets. Spell out imperial units rather than abbreviating them (inches not ").

You can use kcal for energy, but give values in kJ as well.

Give body mass index values as kg/m2.

Use units people are most familiar with (100 ml rather than 1 dl), and be consistent throughout a document (do not use 100 ml in one place and 0.1 litres in another).

Always spell out:

• litre

• microgram (some programs convert µg to mg)

• microsecond

• nanogram.

Repeat units in lists and ranges to avoid ambiguity (5%, 15% and 25%; 5 ml to 15 ml).

#### Date and time

For dates, use the format 4 September 2009. The format 4/9/2009 is okay to save space in a table. Use 2007/08 or 2007 to 2008 for ranges of years.

Write time as 1:30pm.

Write out most units of time in full (30 seconds, 24 hours, 5 years). You can abbreviate ms (millisecond) and more complex units of time (such as 5 m/s [metres per second]). You might want to spell out other units depending on your audience. For example, if you're writing for the public, milligrams might be more understandable than mg.

Use 'a', not per or slashes wherever possible with units ('30 mg a day', 'pulse below 50 beats a minute').

Use weeks of pregnancy, not weeks of gestation.

Use weeks+days if needed for clinical or safety reasons. For example, 'Offer an ultrasound scan to take place between 11+2 weeks and 14+1 weeks to determine gestational age'. If a precise day is not needed, you can just use weeks. For example, 'At the antenatal appointment at 28 weeks, consider a blood test'.

### Symbols

Do not use <, >, ≤, ≥, × (multiply) and = in text except for expressing p values and other measures of significance. You can use them in tables if space is tight. When 'translating' symbols in text, use plain English. For example, say X or more rather than equal to or greater than X.

Only use an ampersand (&) if it forms part of a company name (Johnson & Johnson). A&E is fine but emergency department is usually clearer.

Do not use ™ or ® marks after brand names.

Avoid using forward slashes. Do not use and/or: use just 'or', or 'X or Y, or both'.

Use alpha or alfa, not α (TNF-alpha inhibitor; interferon alfa).