What Is Line?
A line is an old unit for measuring very small lengths. It is smaller than an inch. People used it in printing, watchmaking, and some crafts to measure thickness or size. Today it is mostly replaced by millimeters, but you may still see it in some special fields.
Definition
A line is not a standard unit like the meter. It is a traditional unit, and its exact size changes with place and time. In many English speaking countries one line was usually taken as one twelfth of an inch.
Because one inch is 25.4 millimeters, one English line equals about 2.12 millimeters. In other countries the line was slightly different, but always a very small part of an inch.
So you can think of a line as a tiny piece of an inch used for fine, careful measurements.
History / Origin
The line comes from old European measuring systems. People used the inch as a main small unit, then divided the inch into smaller parts.
- England and the United States: a line was usually 1/12 of an inch.
- France: a similar unit called the ligne came from the old French inch and was about 2.26 millimeters.
- Russia: a line was often taken as 1/10 of an inch, or about 2.54 millimeters.
Workers who needed careful measurements used the line. Printers used lines to measure the thickness of lead strips. Watchmakers used lines to give the size of watch movements. Gun makers and other metal workers also used lines for fine details.
When the metric system and the International System of Units SI became popular, most countries stopped using the line for daily work.
Symbol & Abbreviation
The line does not have one official symbol like m for meter or in for inch. Different trades and languages used different marks.
- In English texts it is often just written in full as line.
- Some writers use a short form like ln or the letter l.
- In French watchmaking the related unit ligne is sometimes written with three small prime marks like ”’.
Because of this mix, if you see the word line you should check the context to know which value is meant.
Current Use Around the World
Today the line is rare. Most people and most science work with millimeters, centimeters, and inches instead. Still, the unit has some limited use.
- Watchmaking and jewelry: in some European watch and jewelry catalogs sizes may be given in lignes, a form of the line used for watch movements.
- History and restoration: people who study old tools, guns, or machines sometimes need to understand lines to read old plans and books.
- Printing history: historians of printing may meet the line when looking at old type setting rules.
In modern engineering, science, and schools the line is almost never used. It survives mostly in older documents and in a few traditional crafts.
Example Conversions
Because the size of a line changed from place to place, the numbers below are common helpful values, not strict rules.
English or US line usually 1/12 of an inch:
- 1 line = 1/12 in ≈ 0.0833 inch ≈ 2.12 mm
- 3 lines ≈ 0.25 inch ≈ 6.35 mm
- 6 lines ≈ 0.5 inch ≈ 12.7 mm
- 12 lines = 1 inch ≈ 25.4 mm
French ligne often used in watchmaking:
- 1 ligne ≈ 2.26 mm
- 10 lignes ≈ 22.6 mm ≈ 2.26 cm
- 12 lignes ≈ 27.1 mm ≈ 2.71 cm
Russian line often 1/10 of an inch:
- 1 line ≈ 2.54 mm
- 4 lines ≈ 10.16 mm ≈ 1.016 cm
To convert from lines to millimeters you can multiply by about 2.1 for the English style line. To convert from millimeters to lines you can divide by about 2.1. Always check which kind of line is meant.
Related Units
The line fits into a family of small length units that are used for fine work.
- Inch in the base unit that the line divides.
- Millimeter mm the modern metric unit used instead of the line.
- Centimeter cm equal to 10 millimeters, also common in daily life.
- Point a very small unit used in printing and digital fonts. In the modern system 1 point is 1/72 of an inch.
- Pica a printing unit equal to 12 points.
When you work with current tools, software, or measuring devices, you will almost always see millimeters, centimeters, inches, points, or picas instead of lines.
FAQs
What is a line in measurement?
A line is an old unit for very small lengths. In many English sources it is 1/12 of an inch, or about 2.12 millimeters. It was used in crafts that needed fine detail.
Is a line part of the metric system?
No. The line is not part of the metric system or the modern International System of Units SI. It belongs to older measuring systems that most countries have now replaced with meters and millimeters.
Why do different books give different sizes for a line?
There is no single global definition of the line. Each country and trade could set its own value. For example, in England a line was usually 1/12 of an inch, in Russia it was often 1/10 of an inch, and in France a related unit the ligne was based on the old French inch.
Where is the line still used today?
The line is still used sometimes in watchmaking, especially in Europe, where the French style ligne can be used to describe watch movement diameter. It may also appear in books about old printing, guns, or machines. In normal school and daily life it is almost never used.
How do I convert lines to millimeters?
First find which kind of line is used. If it is the English type, treat 1 line as about 2.12 millimeters and multiply the number of lines by 2.12. For the French ligne use about 2.26 millimeters. For the Russian line use about 2.54 millimeters.
Should I use lines in new designs or projects?
No. For new work you should use millimeters, centimeters, meters, or inches. These are standard, easy to share, and understood worldwide. Lines are mostly for reading and understanding historical material.
