How Big is 20 mm? Visual Guide With Real Examples
Quick answer: 20 mm is 0.787 inches and 2.0 cm. That is a small measurement, smaller than the width of most adult fingertips, so it is best pictured against tiny everyday objects rather than against a hand or a room.
Exact Conversion
To convert millimetres to inches, divide by 25.4, because one inch is exactly 25.4 mm. So 20 ÷ 25.4 = 0.787 inches. To get centimetres, divide by 10, because there are 10 mm in 1 cm, giving 2.0 cm. Try the mm to inches converter for other values. You can also use the inches to mm converter to go the other way.
| Unit | Value |
|---|---|
| Millimetres | 20 mm |
| Centimetres | 2.0 cm |
| Inches | 0.787 in |
| Metres | 0.02 m |
Real-Life Examples
Because 20 mm is small, the best comparisons are small, familiar things you have probably held. These examples give you a real sense of the size.
- Two centimetres, exactly, because 20 mm make 2 cm.
- The diameter of a large coin, roughly 20 mm across.
- The width of a watch strap in many common sizes.
- The length of a standard paperclip, roughly 20 to 30 mm long depending on the size.
- The diameter of a bottle cap from a small drink bottle.
How to Measure It
Millimetres are too small to judge by eye, so use a ruler with millimetre marks, a set of calipers, or a digital measuring tool. Line the zero mark up exactly with one edge of the object and read the small marks: each one is a millimetre. For a coin or a watch strap, measure twice and take the same reading both times before you cut, drill, or order a part, because a single millimetre of error can matter at this scale.
Common Uses: Where You See This Size
Twenty millimetres is a common size for coins, watch straps, bottle caps, and small fasteners. It is also a frequent size for beads, buttons, and the width of ribbons and cables, where a centimetre measurement would hide the difference between, for example, 18 mm and 22 mm straps.
Common Mistakes to Avoid
The most common mistake is mixing up millimetres and centimetres, which makes a measurement ten times too large or too small. Another is reading the wrong side of a ruler, since many rulers show inches on one edge and centimetres and millimetres on the other. People also guess instead of measuring: 20 mm looks almost nothing on a screen, but in screws, jewellery, and electronics it is a real, working size.
Putting It in Context
It helps to place this size on a ruler you already know. A metric ruler is marked in centimetres, with ten small millimetre marks between each number, so this measurement is only a few of those small marks. That is why it is easy to miscount by one mark, and why measuring twice is worth the few seconds it takes. Always start from zero, keep the ruler still, and read the number twice. Once the reading is right, the conversion is simple arithmetic, and the result will fit the part you are making or ordering.
Frequently Asked Questions
How many inches is 20 mm?
20 mm is 0.787 inches, because 20 ÷ 25.4 = 0.787.
How many centimetres is 20 mm?
20 mm is 2.0 cm, because there are 10 mm in every centimetre.
Is 20 mm bigger than a centimetre?
No, if the value is below 10. Ten millimetres make one centimetre, so anything under 10 mm is a fraction of a centimetre.
How do I measure 20 mm without special tools?
Use a metric ruler and count the small marks between the numbered centimetre marks. Each small mark is one millimetre, so count carefully from zero.
Why do small parts use millimetres instead of inches?
Because millimetres give whole numbers for small sizes. A part that is 0.197 inches is much easier to describe, make, and check as 5 mm.