Leave a space between the number and the unit of measure and use open punctuation (no periods).
For the UK, France, Germany, and Japan, use the metric system (10 cm; 25 kg).
For the US, use the imperial system (10 in.; 25 lbs.).
Use a hyphen if you're using the number with the unit of measure as an adjective (3.4-GHz processor; 2-day workshop).