Rules for Numbers

Rule for numbers in general

  • Do not use numerical numbers at the beginning of a sentence.

    15% of genes … => Fifteen percent of genes …

  • Put a space between numbers and units: 75 kg.

  • Usually use two significant digits for standard deviations and percentages, two decimal places for correlations.

    r = 0.45; r= 0.08; 18%; 1.3%; 0.013%

  • Two decimal digits of the mean and standard deviation should be consistent.

    Correct: 15600 ± 700; 20.020 ± 0.013

    False: 1.6 ± 0.07; 20 ± 13.1


  1. 10以下的数字:one, two, three, four, five, six, seven, eight, nine, ten
    • Martin has two younger sisters and five older brothers.
    • Note: Some style guides recommend spelling out the numbers one to one hundred.
  2. 位于句子开头的数字。
    • Sixty children came to the class trip last year, but this year there were 80.
  3. 分数(通常用破折号连接)
    • About one-third of the class comes from China.
    • Note: However, the exception to this rule is when it is a mixed fraction. We then use numerals (unless it comes at the beginning of a sentence).
    • Example: The recipe calls for cups of nuts.


  1. 10或者10以上的数字。如果是数字的list,要保持一致
    • She has bought about 12 pairs of shoes and 15 dresses in the last three months.
    • Note: When numbers are in a list it is best to keep all the numbers in the list consistent, even if numbers are under 10.
    • Correct: She has four brothers aged 5, 7 12, and 15.
  2. 日期和年份
    • School begins on August 27, 2009.
    • Note: We do not use ordinal numbers (i.e. 1st, 2nd, 3rd) with full dates.
    • Correct: The play is on March 23, 2010.
  3. 百分数
    • According to the latest survey 52% of teachers live in the city.
    • Note: If a percentage begins a sentence, it should be spelled out.
    • Example: Fifty and one-half percent of students walk to school.
  4. 小数
    • There was 0.73 inches of rain last month.


  1. 年代 She lived in San Francisco in the eighties. During the 1980s she lived in San Francisco. She lived in San Francisco in the ‘80s.

  2. 时间

    We usually spell out the time when it is followed by o’clock or when a.m. or p.m. is not mentioned. However, we use numerals when we need to emphasize the exact time and when using A.M. and P.M.

    • Examples: o’clock

    Correct: We have to get up at six o’clock to be on time for school.

    Correct: She gets home around eight in the evening.

    Incorrect: We have to get up at 6 o’clock to be on time for school.

    • Examples: a.m., p.m.

    The accident happened at 8:22 p.m. last night.

    They did not leave the party until 2 a.m.

    We usually spell out noon and midnight instead of writing 12:00 p.m. and 12:00 a.m.

    • Example: We came home around midnight and slept until noon the next day.


Writing rules

Writing Numbers


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