Astonishing numbers: Many writers feel compelled to add adjectives such as ‘jaw-dropping’ or ‘eye-watering’ to even modest figures. Consider whether this is really justified. Similarly, resist the temptation to describe a small change as ‘soaring’, ‘leaping’ or ‘plunging’.
Dates: A common format is Wednesday, April 29, 2009. I suggest you don’t use ‘29th’.
dollars: Give the sterling equivalent of any dollar sum in brackets. However use your judgment and don’t say, for example, ‘She looked a million dollars (£660,000)’. Look up the day’s dollar rate and multiply. To check that you have done it right, you should end up with a larger number of dollars than pounds. All this applies to euros too. I don’t think you would usually give a conversion for any other currency, just give the sterling amount, except if it is unavoidable in a quote. The website https://www.xe.com/currencyconverter/ is a quick and simple converter.
Fewer than/less than: Fewer is used for numbers of people or things, such as ‘fewer than 100 people attended’; less is for unmeasured or overall concepts, as in ‘There is less water in the river’ or ‘There is less money in my bank account’. As Keith Waterhouse sums it up: Fewer can be counted, less cannot.
Fractions: Hyphenate fractions less than one, such as two-thirds of the voters, a two-thirds majority. More than one: Seven and a half years, but the seven-year itch.
Imperial measurements: Use numerals with the abbreviations oz, lb, st, cwt, in, ft. No full points, no plurals, no space between the number and the abbreviation, eg 12st 5lb, 1in. Do not abbreviate acres, miles, pints or gallons. Most British readers would probably prefer acres to hectares. Multiply hectares by 2.47 to convert to acres. To check that you have done it right, you should end up with more acres than hectares.
Metric measurements: Although many do not like metric measurements, they are a fact of life, and younger people may not be familiar with imperial. I suggest you give both, but it is your choice which to give first, and which to give in brackets afterwards. Be consistent, and never mix decimals with imperial measurements. Write 3ft 9in rather than 3.75ft, or 6lb 8oz not 6.5lb. Here is an example of how not to do it from the Sunday Telegraph, November 2, 2014, on the topic of the Virgin spacecraft crash: 'It is carried to 50,000ft by a jet aircraft and then detaches, firing its solid-fuel rocket to send it up to 100 kilometres (62 miles) . . . ' You need your calculator to sort that out.
More than/over: ‘More than’ is generally for quantities, ‘over’ is for ages. So ‘There are more than 100 items in the basket’ but ‘She is over 21’. This is not a hard and fast rule, though.
One in three etc: I acknowledge help from the Guardian style book here. All my working life I have believed that ‘one in three’ etc should be treated as singular, eg ‘one in three children leaves school unable to count’. However the Guardian points out that grammatically we are not talking about the noun ‘one’ but the noun phrase ‘one in three’ signifying a group of people. It is the same concept as one-third, 33 per cent, or three out of ten, all of which would be followed by the plural formula ‘ … (of) children leave school unable to count’. So I have revised my ideas and suggest treating ‘one in three’ etc as plural. To back up my theory, here is an intro from the Daily Mail in September 2010: ‘One in four women faces an impoverished retirement because they are relying on their husband’s pension.’ The sub, as I would have done hitherto, has treated ‘one in four’ as singular and paired that with the singular ‘faces’. However things go a bit awry with the plural ‘they’ and ‘their’. To be consistent, it would need to say: ‘One in four women faces an impoverished retirement because she is relying on her husband’s pension.’ That reads most oddly to me. The only way to make it grammatical and read well, it seems to me, is to treat ‘one in four’ as plural, thus: ‘One in four women face an impoverished retirement because they are relying on their husbands’ pension.’
Here is another example from the Times, May 2015: 'Nearly one in three savers plans (singular) to use their (plural) new pension freedoms to splash out on expensive cars or holidays . . . Of these, almost one in eight plan (plural) to take the lot to spend on indulgences . . . less than (should be fewer than) one in ten retiring savers are (plural) opting to buy an annuity . . . ' The lesson here is to decide on a format and stick to it.
per cent/percentage points: There is widespread confusion between percentage and percentage points, so here's the distinction between the two. Percentages are a way of expressing a proportion out of 100. Percentage points are used to express the difference between percentages. Imagine that 20 out of 50 people understand this rule – that's 40 per cent. Then, after reading this, that number rises to 40 out of 50 – or 80 per cent. That is a rise of 40 percentage points, not 40 per cent. (It's actually a rise of 100 per cent, because the number has doubled). With more complicated increases/decreases, eg from 17 per cent to 24 per cent, working out the percentage change is fiendishly difficult, so it's easier just to say there has been a rise of seven percentage points. The website http://www.percentagecalculator.net/ is a painless way to calculate or check percentages.
Roman numerals: These do come up and it is handy to know how to use them, or at least to be able to spot if they are wrong. Note that for a Roman 1 you use a capital I:
I = 1
V = 5
X = 10
L = 50
D = 500
M = 1,000
Using these seven letters you can express any number except 0. The principle is that you use the biggest symbol that is under the number you need, plus up to three of any symbol in a row, and when you need a fourth you ‘subtract’ one from the next letter, placing it in front of that letter. Thus 13 is XIII (ten, plus one, plus one, plus one) and 14 is XIV (ten, minus one, five). 823 is DCCCXXIII (five hundred, one hundred, one hundred, one hundred, ten, ten, one, one, one). 924 is DCDXXIV (five hundred, minus one hundred, five hundred, ten, ten, minus one, five). Publication dates are sometimes given in Roman numerals, particularly on films. For example 1959 is MCMLIX (one thousand, minus one hundred, one thousand, fifty, minus one, ten) and 2014 is MMXIV (one thousand, one thousand, ten, minus one, five).
Stock market index: Do not put the usual comma to denote thousands. So ‘The FTSE stood at 5678’, not 5,678.
Sums of money are singular. For example you would say ‘Several million pounds has been spent on the project’, not ‘have been spent’. Weights should also be treated as singular, eg ‘4oz of cannabis was found in his pocket’ or ‘450million tons of good food is wasted each year’. Periods of time are usually singular, as in ‘Ten years is a long time’, not, as recently seen, ‘Two years are enough’.
Temperatures: We should now all be pretty used to Celsius, so use that as the main measure but give the Fahrenheit equivalent in the first reference, though maybe not every time. Thus: ‘The South can expect temperatures of 28C (82F) at the weekend, but next week it will be a cooler 16C.’ Use cap C and F (see Medical and Scientific Matters for more on this).
totals: Avoid totals such as ‘Six men were jailed for a total of 23 and a half years’. This is meaningless. Much better to say ‘Six men were given jail terms ranging up to ten years’. A good recent example was the Hatton Garden raid gang, aged 42 to 76. Several news organisations had headings about their combined age of 490 without giving the reader the tool needed for mental arithmetic, ie the number of men in the dock. I would not set readers a maths test, but highlight the fact that several were pensioners. The Sun came up with the brilliant ‘Diamond Wheezers’.