it depends on about how big it is
but i would guess meters or centimeters
kilometer, meter, centimeter, millimeter mile, foot, inch
Metre.
The meaning of linear dimension is to measure in a straight line with the units. Which are Kilometer, Meter, decimeter, centimeter and lastly millimeter.
millimeter
The millimeter. It is 10 times smaller than a centimeter.
millimeter
the nearest millimeter
kilometer
A millimeter is one-tenth of a centimeter. This means there are 10 millimeters in one centimeter. Millimeters are commonly used to measure smaller lengths, while centimeters are used for slightly larger measurements.
Length
When you say "what is after", I assume you mean the next smallest. while a millimeter is 1x10-3 meters, the next smallest most commonly used unit of measure is the micrometer which is 1 x 10-6 meters.
Of the four units of measure in question, the millimeter (mm) is the shortest. In comparison: 1 inch = 25.4 mm; 1 centimeter = 100 mm; 1 ft = 12 inches.