Nouns with decimals

Question:

Should I use a singular or plural noun with decimals below 1? Is it correct to write 0.5 hour? Or, is it 0.5 hours?

Answer:

In Practical English Usage (1995), Michael Swan tells us that singular nouns are generally used with decimals (and fractions) below 1. For example:

• 0.5 hour (or one half hour)
• 0.1625 cm (or zero point one six two five of a centimetre)

Decimals (and fractions) over 1 are followed directly by a plural noun, as in the following examples:

• 1.5 hours (or one and one half hours)
• 1.3 millimetres (or one point three millimetres)