How the BIPM Declared War on the Centimeter — and Lost
The SI Brochure is the constitution of the metric system, published by the BIPM in Sèvres, France. Its 9th edition (2019) is unambiguous: "The centimeter is not recommended for use in science and technology." The BIPM's argument is practical. When a drawing says "15," is that 15 meters, 15 centimeters, or 15 millimeters? In the BIPM's preferred scheme, there are only three standard subdivisions of the meter: the meter itself, the millimeter (10⁻³ m), and the kilometer (10³ m). Every engineering dimension should be expressed in one of these three. No centimeters. No decimeters. No decameters. Just meters, millimeters, and kilometers — each spaced by a factor of 1,000.
This is not a new argument. In 1960, the 11th General Conference on Weights and Measures (CGPM) adopted the International System of Units and recommended that prefixes should be used in steps of 10³. The prefixes centi- (10⁻²), deci- (10⁻¹), deca- (10¹), and hecto- (10²) were tolerated but discouraged. The CGPM wanted a clean system: kilo, mega, giga, tera on one side; milli, micro, nano, pico on the other. The centimeter was supposed to fade away.
It did not fade away. The centimeter survived because the BIPM's recommendation solves an engineering problem — unit ambiguity — but creates a human one. 1700 mm is correct by SI convention. 170 cm is what a human being actually says. Four significant digits versus three. "Seventeen hundred millimeters" versus "one seventy centimeters." The centimeter maps to the human scale: a finger is about 1 cm wide, a hand is about 10 cm across, a human is about 170 cm tall. The millimeter is too fine for everyday use; the meter is too coarse. The centimeter is just right, and no standards body can legislate it away.
Three Places Where the Centimeter Rules — and One Where It's Dangerous
- Human height (170 cm): Every country except the United States reports human height in centimeters. Medical records in France, Japan, Brazil, and Australia all use cm. The WHO growth charts for children are in cm. No doctor has ever told a parent their child is "1,025 mm tall" — that is technically correct by the BIPM's rulebook, and it is also absurd.
- Clothing and textiles (chest 92 cm, waist 76 cm): The global apparel industry — from fast fashion to luxury tailoring — uses centimeters for body measurements. A size 40 jacket has a 100 cm chest. Pattern cutting software exports to cm. The millimeter is used only at the sewing machine level (seam allowances of 10 mm).
- Furniture and interiors (table height 75 cm, seat depth 45 cm): IKEA dimensioning is entirely in centimeters. A BILLY bookcase is 80 cm wide, 202 cm tall, 28 cm deep. The metric construction industry outside North America dimensions architectural interior plans in cm — a 90 cm door, a 60 cm counter depth.
- Engineering drawings — danger zone: A structural drawing from a European firm dimensions beams in mm (HEA 200 = 200 mm deep). An interior design drawing from the same project dimensions walls in cm. A 200 mm beam and a 200 cm wall are both "200" — one is a structure, the other is a partition. The cm-to-mm confusion on a single project can produce a wall 10× too thick or a beam 10× too thin. This has happened. Always check which unit the drawing assumes.
Common Meters to Centimeters
| Meters | Centimeters (exact) | Where you see this length |
|---|---|---|
| 0.01 m | 1 cm | Width of a fingertip. The smallest mark on most rulers. |
| 0.3 m | 30 cm | Standard school ruler. One foot (30.48 cm). |
| 1 m | 100 cm | Doorknob height. A guitar. Meter stick. |
| 1.70 m | 170 cm | Average human height globally. |
| 2 m | 200 cm | Standard interior door height in metric countries. |
| 2.5 m | 250 cm | Standard residential ceiling height. |
| 100 m | 10,000 cm | Olympic sprint distance. 10,000 cm = 100 m = 0.1 km. |
Frequently Asked Questions
How do you convert meters to centimeters?
Multiply the number of meters by 100. Formula: cm = m × 100. The SI prefix centi- means one hundredth (10⁻²), so 1 m = 100 cm exactly. For example, 1.75 m × 100 = 175 cm. This conversion is exact — there is no rounding or approximation, because both units are defined within the same coherent SI system.
Why don't engineers use centimeters?
The BIPM's SI Brochure explicitly recommends the millimeter (mm) as the standard subdivision of the meter for technical work. The reason: avoiding ambiguity. A drawing labeled "150" in mm means 150 mm (0.15 m). The same "150" in cm means 150 cm (1.5 m) — a factor-of-10 difference. Civil engineering firms standardize on mm; a 450 mm beam is always 450. The centimeter's survival is a consumer phenomenon — it's the right scale for human-sized objects, and no standards document has been able to overcome that.
How tall is the average person in centimeters?
Global average adult height is approximately 170 cm (1.70 m) for males and 158 cm (1.58 m) for females, though this varies significantly by region. The Netherlands has the tallest population, with an average male height of approximately 183 cm (1.83 m). The centimeter is the standard unit for human height measurement in every country except the United States, which uses feet and inches (e.g., 5'9" ≈ 175 cm). Medical records, WHO growth charts, and sports statistics all use centimeters.
Engineering Context
The meter-to-centimeter conversion (1 m = 100 cm) is arithmetically trivial — multiplication by 100. But the engineering risk is not the math; it's the domain convention mismatch. A civil engineering firm in Germany dimensions structural drawings in mm: a concrete column is labeled "300 × 300" meaning 300 mm × 300 mm (0.3 m × 0.3 m). An interior architect in the same building dimensions partition walls in cm: a wall is labeled "10" meaning 10 cm (100 mm). When the architect's drawing says "10" and the structural engineer reads it as 10 mm, the wall becomes a sheet of paper. When the engineer's drawing says "300" and the architect reads it as 300 cm, a 0.3 m column becomes 3 m thick. The fix is mandatory unit annotation on every drawing sheet — a note that says "All dimensions in mm unless otherwise noted" or "All dimensions in cm." The most expensive cm/mm errors in construction history have come from drawings that omitted this note. If you're working in BIM, set the project units at kickoff and lock the template. For more on unit conventions across disciplines, see the Length Conversion Guide.