IN either unit: it depends on the precision that you require.
milimeters
usually by mm unless it is large enough to warrant being measured by cm.
The height of a human is usually measured in cm.
Three science students measured the lengths of their lab specimens the longest specimen would be 20.3 cm. This is because 25 mm is 2.5 cm, and 201 mm is 20.1 cm.
1 cm = 10 mm 8 cm = 80 mm 80 cm = 800 mm 86 cm = 860 mm 86.3 cm = 863 mm 86.36 cm = 863.6 mm
1 cm = 10 mm 2 cm = 20 mm . . . 9 cm = 90 mm 10 cm = 100 mm 20 cm = 200 mm 30 cm = 300 mm
1 cm = 10 mm → 3.5 cm = 3.5 × 10 mm = 35 mm
neutrons are so small they could not be measured in cm. They are like 1/1000 of a mm.
1 cm = 10 mm 2 cm = 20 mm . . 10 cm = 100 mm . . 15 cm = 150 mm
10 mm = 1 cm . 100 mm = 10 cm . 1,000 mm = 100 cm 2,000 mm = 200 cm . 4,000 mm = 400 cm
10 mm = 1 cm 20 mm = 2 cm 200 mm = 20 cm 240 mm = 24 cm 244 mm = 24.4 cm
10 mm = 1 cm 100 mm = 10 cm 1,000 mm = 100 cm 3,000 mm = 300 cm 3,500 mm = 350 cm