There are one thousand millimetres in a metre the prefix milli- stands for thousandths. So 0.25 metres is 0.25 x 1000 millimetres, which is 250 mm.
10 mm = 1cm 1 in = 2.54 cm 1 in = 25.4 mm
90 mm
16.5 mm
6450 mm
100 mm
153 mm
760 mm
50.8 mm
304.8 mm
8500 mm
135 mm.
885 mm