The millimetre (international spelling as used by the International Bureau of Weights and Measures; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the metric system, equal to one-thousandth of a meter, which is the SI base unit of length. Therefore, there are one thousand millimeters in a meter. There are ten millimeters in a centimeter.

A centimetre (international spelling as used by the International Bureau of Weights and Measures; symbol cm) or centimeter (American spelling) is a unit of length in the metric system, equal to one-hundredth of a metre, one 100th of a meter, equivalent to 0.3937 inches. The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.
1 centimetre = 10 millimetres
= 0.01 metres
= 0.393700787401574803149606299212598425196850 inches
(There are exactly 2.54 centimetres in one inch.)

The decimeter (SI symbol dm) is a unit of length in the metric system, equal to one-tenth of a meter (the International System of Units base unit of length), ten centimeters or 3.937 inches.

The metre (Commonwealth spelling and BIPM spelling[1]) or meter (American spelling[2]) (from the French unit mètre, from the Greek noun μέτρον, "measure") is the base unit of length in the International System of Units (SI). The SI unit symbol is m.

The foot (pl. feet; abbreviation: ft; symbol: ′, the prime symbol) is a unit of length in the imperial and US customary systems of measurement. Since the International Yard and Pound Agreement of 1959, one foot is defined as 0.3048 meters exactly. In customary and imperial units, the foot comprises 12 inches and three feet compose a yard.

The yard (abbreviation: yd) is an English unit of length, in both the British imperial and US customary systems of measurement, that comprises 3 feet or 36 inches. Since 1959 it is by international agreement standardized as exactly 0.9144 meters.