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Coin Size Checker — Check Diameter & Thickness

As of: 05/30/2026, 00:06 · Update interval: 1 minute ·
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The coin size checker compares the diameter and thickness of your bullion coin against the official target values from the mints. Choose from 129 verified coins and enter your measurements. The traffic light system instantly shows whether the dimensions are within manufacturing tolerances. Deviating dimensions can indicate counterfeits — especially in combination with a weight check, since incorrect material density always leads to altered dimensions.

Traffic Light System

OK ≤ 0.5%
Borderline 0.5–1%
Suspicious > 1%
Below target < target & > 1%

Tips for Size Checking

  • 1. Digital caliper with ±0.02 mm accuracy.
  • 2. Zero the caliper (ZERO button) before each measurement.
  • 3. Measure diameter across the center, rotate 3 times.
  • 4. Measure thickness in the center, not at the edge.
  • 5. For a complete check: combine with the Authenticity Checker including weight.

Note: Dimensions alone are not sufficient for authenticity testing. Combine the size check with a weight check and further tests (magnet, ring test) for a reliable result.

Authenticity Checker

Complete check with weight, diameter and thickness.
Weight Checker

Detailed weight check with tolerances.
Melt Value Calculator

Material value for bars, coins and jewelry.

Why Measure Dimensions?

The weight check is the most well-known authenticity test — but it has a weakness: Tungsten. At 19.25 g/cm³, tungsten's density is only 0.36% below that of gold (19.32 g/cm³). A tungsten counterfeit can hit exactly the target weight while the scale raises no alarm.

This is exactly where size checking comes in: Since tungsten has a slightly lower density, a tungsten core must occupy slightly more volume at identical weight. This manifests in measurable deviations in diameter or thickness. Combine both tests, and counterfeiting becomes physically nearly impossible.

The Tungsten Problem

Tungsten has almost the same density as gold. A counterfeit with a tungsten core passes the weight check easily — only the dimensions reveal the difference.

Cross-Validation

When weight and dimensions match simultaneously, every counterfeit material except pure gold is ruled out. Start complete check

Size Checking at a Glance

Size checking is essential against tungsten counterfeits — tungsten has almost identical density to gold, but the dimensions must differ. For the detailed guide with all tests, visit our Authenticity Check Guide.

1 Zero

Close calipers, press ZERO button. Keep measuring surfaces clean.

2 Diameter

Measure across the center, rotate 3 times (60&deg;), calculate average.

3 Thickness

Measure in the center, not at the edge. Measure 3 times, calculate average.

Manufacturing Tolerances

Diameter ±0,1 mm
Thickness ±0,15 mm

Thickness varies more (striking pressure, material distribution)

Recommended Equipment

Digital Caliper 15–25 €
Accuracy ±0,02 mm

150 mm measuring range, ZERO function, CR2032 battery

Coin Diameter Thickness Weight
🇿🇦 Krugerrand 1 oz
32.77 mm 2.84 mm 33.930 g
🇨🇦 Maple Leaf 1 oz
30.00 mm 2.87 mm 31.103 g
🇦🇹 Philharmonic 1 oz
37.00 mm 2.00 mm 31.103 g
🇺🇸 American Eagle 1 oz
32.70 mm 2.87 mm 33.931 g
🇬🇧 Britannia 1 oz
32.69 mm 2.55 mm 31.103 g
🇨🇳 China Panda 30g
32.00 mm 2.68 mm 30.000 g
🇦🇺 Kangaroo 1 oz
32.10 mm 2.65 mm 31.103 g
🇨🇦 ML Silver 1 oz
38.00 mm 3.29 mm 31.103 g
🇦🇹 Phil. Silver 1 oz
37.00 mm 3.20 mm 31.103 g
🇺🇸 AE Silver 1 oz
40.60 mm 2.98 mm 31.103 g

Dimensions alone are not enough. Tungsten counterfeits can have correct dimensions and correct weight. Always combine dimensions with the ring test and magnet test.

Measuring Instruments Compared

Not every measuring device is equally suited for coin checking. The key factors are accuracy, handling, and value for money. Here are the four most common options compared.

Recommendation

Digital Caliper

15–25 EUR · ±0.02 mm
+ Easy reading, ZERO function, measures diameter and thickness
+ Best value for money for coin checking
− Not as precise as a micrometer for thickness measurement

Micrometer / Outside Micrometer

25–60 EUR · ±0.01 mm
+ Highest accuracy for thickness measurement (±0.01 mm)
+ Constant measuring pressure via ratchet
− Measures only thickness, not diameter (measuring range 0–25 mm)
− More expensive and specialized than calipers

Coin Sizing Gauges (Fisch Test)

20–40 EUR · Pass/Fail
+ Instant result: coin fits or doesn't fit
+ No reading required, very easy for beginners
− Only for specific coin types — separate gauge needed for each
− No exact measured value, only pass/fail indication

Ruler / Smartphone Apps

0–5 EUR · ±0.5–1 mm
+ Immediately available, no acquisition costs
− Far too inaccurate for counterfeit detection (±0.5–1 mm)
− Thickness measurement practically impossible
− Not suitable for authenticity checking

Size Comparison of Coin Series

One ounce of gold is always 31.103 g — but not always the same size. Alloy and fineness determine the density and thus the volume. The Krugerrand (22 carat, with copper) needs more space than the pure Maple Leaf (24 carat). And the Philharmonic? Wide and flat.

Diameter: 1 oz Gold Coins Compared

🇦🇹 Philharmonic
37.00 mm
🇿🇦 Krugerrand
32.77 mm
🇺🇸 American Eagle
32.70 mm
🇬🇧 Britannia
32.69 mm
🇦🇺 Kangaroo
32.10 mm
🇨🇳 China Panda
32.00 mm
🇨🇦 Maple Leaf
30.00 mm
🇦🇹

Largest: Philharmonic

Diameter 37,00 mm
Thickness 2,00 mm
Fineness 999,9/1000

Wide and flat — 23% more diameter than the Maple Leaf

🇨🇦

Smallest: Maple Leaf

Diameter 30,00 mm
Thickness 2,87 mm
Fineness 999,9/1000

Compact and thick — same fineness, 44% more thickness than the Philharmonic

Density and Geometry

Every metal has a fixed ratio of mass to volume — the density. At the same weight and same diameter, a different material inevitably changes the thickness. This is exactly what makes size checking so effective.

Cylinder Formula for Coin Thickness

Thickness = Mass / (Density × π × (Diameter/2)²)

Simplified — real coins have relief and rim that slightly alter the volume.

How thick would a fake Krugerrand be?

Assumption: 33.93 g and 32.77 mm diameter (like genuine), but made from different material.

Material Density Calculated Thickness Deviation
Gold (22 Kt) 17,80 g/cm³ 2,84 mm —
Wolfram 19,25 g/cm³ 2,63 mm −0,21 mm
Blei 11,34 g/cm³ 4,47 mm +1,63 mm
Kupfer 8,96 g/cm³ 5,65 mm +2,81 mm
Zink 7,13 g/cm³ 7,10 mm +4,26 mm

Everything except tungsten is immediately obvious. Lead, copper and zinc produce deviations of over 1.5 mm — you can feel that with your fingers. Only tungsten reaches −0.21 mm, and even that is clearly outside the manufacturing tolerance of ±0.15 mm.

Temperature Effects on Coin Dimensions

Metals expand with heat — but how much does this affect coins? The answer: barely measurable, but good to know.

Calculation Example: Krugerrand

Thermal expansion coefficient gold 14,2 × 10⁻⁶ /°C
Temperature difference +30 °C
Diameter change +0,014 mm

32.77 mm × 14.2 × 10³⁄°C × 30 = 0.014 mm

Practical Tip

Let the coin and caliper acclimatize at room temperature (20°C) for at least 15 minutes before measuring. This avoids thermal distortions — even though the effect is minimal.

Negligible in practice

Wear and Tear

Coins are not laboratory objects — they are handled, stacked and transported. Circulation marks change the dimensions, especially on older or softer coins.

Diameter Wear

Minimal. The diameter hardly changes through wear, as the rim (edge) provides most protection. Even on old circulated coins it remains nearly constant.

Thickness & Relief

More affected. The highest relief points wear down, making the coin measurably thinner. On heavily circulated pieces, the thickness can be 0.1–0.2 mm below the new condition.

Alloy Hardness

22-carat coins (916.7/1000 like Krugerrand, Eagle) are significantly harder due to their copper content than 24-carat coins (999.9/1000 like Maple Leaf, Philharmonic) and wear more slowly.

For older coins: Accept more generous tolerances for thickness. A 1970 Krugerrand can be 0.1 mm thinner than a brand new one — that is wear, not counterfeiting. When in doubt, the weight check helps as a cross-reference.

Coin Capsules and Measuring

Many bullion coins are supplied in plastic capsules. Should you remove the coin for measuring? Both approaches have pros and cons.

Remove from Capsule

+ Exact measurement without material addition
+ Diameter and thickness directly comparable with target values
− Risk of scratches from caliper (steel on gold)
− Fingerprints and moisture can cause patina

Measure in Capsule

+ Coin stays protected, no risk of value reduction
− Capsule wall adds 1–2 mm per side to diameter
− Capsule thickness varies by manufacturer (0.5–1.5 mm per side)
− Inaccurate: play in the capsule distorts thickness measurement

Practical Tip

Remove the coin from the capsule for the initial check — but wear cotton gloves and place the coin on a soft cloth. Close the caliper gently (no clamping pressure). This gives you precise values without risk of damage. For later control measurements, measuring in the capsule is sufficient as a plausibility check.

Frequently Asked Questions About Coin Size Checking

Which caliper do I need?
A digital caliper with 150 mm measuring range and ±0.02 mm accuracy is ideal for coin checking. Good models cost 15–25 EUR and are battery-powered (CR2032). Look for a ZERO function for zeroing and stainless steel measuring surfaces for durability. Analog calipers with vernier scales are also suitable but require more practice when reading.
How accurate are the target dimensions from the mints?
The target dimensions are nominal design values, not measurements of individual coins. Mints typically do not publish official tolerances for dimensions (unlike weight). From manufacturing practice, diameter tolerances of approximately ±0.1 mm and thickness tolerances of approximately ±0.15 mm result. Our tool uses conservative tolerances (±0.3% diameter, ±0.5% thickness) to avoid falsely marking genuine coins as suspicious.
My coin is 0.1 mm too thick — is that normal?
A deviation of 0.1 mm in thickness is in most cases completely normal and within manufacturing tolerances. Thickness varies more than diameter because it depends on striking pressure and material distribution in the blank. The measuring point also affects the result: at the edge, a coin is often 0.1–0.2 mm thicker than in the center. Therefore, always measure in the center.
Why is the thickness tolerance larger than the diameter tolerance?
The diameter is determined by the blank (the planchet), which is machine-stamped to exact dimensions. Thickness, however, is only created during the striking process: depending on striking pressure, blank quality, and die wear, the material distribution can vary slightly. Additionally, material spreads during striking — the edge is pushed slightly outward, and the center can become slightly thinner.
Can a counterfeit have the correct dimensions?
Yes, but only with tungsten-core counterfeits. Tungsten at 19.25 g/cm³ has an almost identical density to gold (19.32 g/cm³). Therefore, weight and dimensions can match simultaneously. Such counterfeits are, however, complex and expensive to produce. They can be detected through the ring test (different elasticity) and the magnet test (tungsten is weakly paramagnetic).
Should I check diameter or thickness first?
Start with the diameter, as it is easier to measure (the coin just needs to be placed between the jaws). The diameter also has tighter manufacturing tolerances and is therefore more informative. Thickness should follow as the second measurement — it requires a bit more care with positioning (center vs. edge) but provides additional confidence.
Micrometer or caliper — which is better?
For pure thickness measurement, the micrometer (outside micrometer) with ±0.01 mm is more accurate than calipers (±0.02 mm). Calipers, however, are more versatile: they measure both diameter and thickness and are easier to use. For most collectors and investors, the digital caliper is the better all-round tool. A micrometer is worthwhile as a supplement if you need maximum precision for thickness.
Can I reliably measure a coin in its capsule?
Only to a limited extent. The capsule wall adds 1–2 mm per side to the diameter, and capsule thickness varies by manufacturer. Thickness measurement in the capsule is particularly inaccurate, as air between coin and capsule lid creates play. For a reliable initial check, you should remove the coin — with cotton gloves on a soft surface.
Why is a Krugerrand larger than a Maple Leaf?
The Krugerrand is made from a 22-carat alloy (91.67% gold, 8.33% copper) with a density of approximately 17.8 g/cm³. The Maple Leaf is made of 24-carat fine gold (19.3 g/cm³). At the same gold content (1 oz), the Krugerrand is heavier (33.93 g vs. 31.10 g) and has a larger volume due to the lower alloy density — hence 32.77 mm instead of 30.00 mm diameter.
How can I calibrate or check my caliper?
Close the caliper and press the ZERO button — the display must show exactly 0.00 mm. Then check with a gauge block or calibration standard (e.g. 25.00 mm) whether the reading is correct. Without a calibration block: measure a known object (e.g. a euro coin: 1 euro = 23.25 mm diameter). If the caliper deviates by more than ±0.03 mm, replace the battery or the device.

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