Hyphens in suspended compound adjectives

Question:

Are the hyphens placed correctly in the following sentence? Should centimetre be written out? For example:

• A one- to two-centimetre-deep layer of thatch is good for your lawn.

Answer:

The Canadian Style is a handy source to have for these types of style questions.

First of all, the hyphens are placed correctly in this suspended compound because the phrase one- to two-centimetre-deep is an adjective modifying layer.

Second, The Canadian Style states as follows:

• SI [International System of Units] usage prescribes that both numeral and unit name be written in full or that both be abbreviated: two metres or 2 m.

Therefore, it is better to write centimetre than cm in your example: A one- to two-centimetre-deep layer…