How long is a Roman mile in km?

The Roman mile (mille passuum — 'a thousand paces') equals 1,480 meters or approximately 1.48 km. It was defined as 1,000 double-steps (passus), each passus being 5 Roman feet (pedes). The modern mile of 1,609 meters is about 8.7% longer than the Roman mile.

What is a Roman foot in cm?

The Roman foot (pes) measured 296 mm or 29.6 cm — slightly shorter than the modern foot of 30.48 cm. It was divided into 12 unciae (the origin of 'inch') and was the base unit for most Roman linear measurements.

What is the origin of the word inch?

The word 'inch' derives from the Latin 'uncia', which was 1/12 of a Roman foot (pes). One Roman uncia of length = 24.67 mm, close to the modern inch of 25.4 mm. The same Latin root 'uncia' also gives us the word 'ounce' — because an uncia of the Roman pound (libra) was 1/12 of the total weight.

Ancient Roman Measurement Units: Length, Weight & Modern Equivalents

The Roman System of Length

Roman engineers built roads, aqueducts, and buildings across three continents using a consistent system of measurement. The base unit was the pes (Roman foot), from which all other lengths derived. Unlike modern metric prefixes, Roman units used body-part names and practical references like the double-step.

Roman Unit	Latin Meaning	Modern Metric	Modern Imperial
Digitus	Finger width	18.5 mm	0.73 in
Uncia	Twelfth (of a foot)	24.7 mm	0.97 in
Palmus	Palm width (4 digits)	74.0 mm	2.91 in
Pes	Foot (12 unciae)	296 mm (29.6 cm)	11.65 in
Cubitum	Elbow (1.5 pedes)	444 mm (44.4 cm)	17.5 in
Gradus	Step (2.5 pedes)	740 mm (74 cm)	29.1 in
Passus	Double-step (5 pedes)	1.48 m	4.86 ft
Actus	Field measure (120 pedes)	35.5 m	116.4 ft
Mille passuum	Thousand paces	1,480 m (1.48 km)	4,856 ft (0.92 mi)

Roman Weight Units

The Roman weight system centered on the libra (pound), divided into 12 unciae. This 12-part division is the origin of the Troy weight system still used for precious metals, where 1 Troy pound = 12 Troy ounces.

Roman Unit	Subdivision	Grams	Modern Equivalent
Siliqua	1/1728 libra	0.19 g	~3 grains
Scripulum	1/288 libra	1.14 g	~17.6 grains
Uncia	1/12 libra	27.3 g	0.96 oz avoirdupois
Libra	12 unciae	327.45 g	11.5 oz (0.72 lbs)

Roman Measurement Legacy in Modern Language

Roman units did not disappear — they evolved into the words we use today:

Inch — from Latin uncia (1/12 of a foot). The modern inch is 25.4 mm vs. the Roman uncia's 24.7 mm.
Ounce — also from uncia (1/12 of a pound). The word traveled through Old French once into English.
Pound — from libra pondo ("a pound by weight"). The chemical symbol for pound (lb) comes from libra.
Mile — from mille passuum ("a thousand paces"). The Roman mile (1.48 km) was later adjusted to 1,760 yards (1.609 km) in Tudor England.
Acre — derived partly from the Roman actus field measurement concept.

Convert modern length units with our length converter.