Common Coin Sizes by Country — A Visual Reference Guide

Coins are one of the most accessible measurement references. You probably have several in your pocket or on your desk right now. Since each denomination has standardized dimensions, a coin can serve as a quick ruler substitute or a calibration tool for on-screen measurement.

Here are the exact dimensions of commonly used coins from six countries, all verified against official mint specifications.

United States

Coin	Diameter (mm)	Diameter (inches)	Thickness (mm)
Penny (1¢)	19.05	0.750	1.52
Nickel (5¢)	21.21	0.835	1.95
Dime (10¢)	17.91	0.705	1.35
Quarter (25¢)	24.26	0.955	1.75
Half Dollar (50¢)	30.61	1.205	2.15
Dollar ($1, Sacagawea)	26.50	1.043	2.00

The US quarter is the most commonly used for calibration because it's the most widely circulated coin with a convenient size — large enough for precise alignment but small enough for phone screens.

European Union (Euro)

Coin	Diameter (mm)	Diameter (inches)	Thickness (mm)
1 cent	16.25	0.640	1.67
2 cent	18.75	0.738	1.67
5 cent	21.25	0.837	1.67
10 cent	19.75	0.777	1.93
20 cent	22.25	0.876	2.14
50 cent	24.25	0.955	2.38
€1	23.25	0.915	2.33
€2	25.75	1.014	2.20

The €1 coin is recommended for calibration. Fun fact: the €1 and the US quarter are nearly identical in diameter (23.25 mm vs 24.26 mm) — only 1 mm apart.

United Kingdom

Coin	Diameter (mm)	Diameter (inches)	Thickness (mm)
1p	20.3	0.799	1.52
2p	25.9	1.020	1.85
5p	18.0	0.709	1.77
10p	24.5	0.965	1.85
20p	21.4	0.843	1.70
50p	27.3	1.075	1.78
£1	23.43	0.922	2.80
£2	28.4	1.118	2.50

The current £1 coin (introduced in 2017) is 12-sided but fits inside a 23.43 mm circle. Its unique shape makes alignment slightly trickier than round coins, but the diameter measurement still works.

India

Coin	Diameter (mm)	Diameter (inches)	Thickness (mm)
₹1	22.0	0.866	1.45
₹2	25.0	0.984	1.50
₹5	23.0	0.906	1.90
₹10	27.0	1.063	2.00
₹20	27.0	1.063	2.20

The ₹5 coin offers a good balance of size and availability for calibration use.

Indonesia

Coin	Diameter (mm)	Diameter (inches)	Thickness (mm)
Rp 100	23.0	0.906	1.60
Rp 200	25.0	0.984	1.80
Rp 500	27.0	1.063	2.00
Rp 1,000	24.0	0.945	2.00

The Rp 1,000 coin is widely available and close in size to the US quarter.

Turkey

Coin	Diameter (mm)	Diameter (inches)	Thickness (mm)
5 kuruş	17.5	0.689	1.25
10 kuruş	18.5	0.728	1.40
25 kuruş	20.5	0.807	1.45
50 kuruş	23.85	0.939	1.65
₺1	26.15	1.030	1.95

The ₺1 coin is the most practical for calibration due to its larger diameter.

Why Coins Work for Calibration

Coins make decent calibration references because:

1. Standardized dimensions — minted to tight tolerances, usually ±0.1 mm
2. Universally available — wherever you are, local coins are within reach
3. Rigid and flat — unlike paper, coins don't bend or deform
4. Circular shape — easy to align against a reference circle on screen

The main limitation compared to a credit card: coins are smaller, so alignment errors have a proportionally larger impact. A 0.5 mm alignment error on a 24 mm coin is 2.1%, while the same error on an 85.6 mm credit card is only 0.6%.

For the best accuracy, use a credit card when available. Use a coin when a card isn't handy.

Calibrate with Your Local Coin

Screen Ruler Online supports calibration with coins from all six countries listed above. Select your local coin, place it on the screen, adjust the slider, and you're measuring accurately in seconds.

Don't see your country's coin? Use a credit card instead — it's the same size worldwide.

Once calibrated, the same screen also runs the online protractor for angles and the random spinner for picking — see the full tools page for the rest of the free utilities.