Open any coin catalogue — printed or online — and two numbers appear beside nearly every issue: weight in grams and diameter in millimetres. They are the only facts about your coin that you can produce yourself, today, with kitchen-adjacent equipment. The identification guide ends at "compare against published specifications"; this guide is how you produce the numbers that comparison needs.
Measured values are evidence, not proof. A coin matching its specification supports a candidate; a coin far off it raises questions about the identification, the coin's wear, or its genuineness — the fakes guide covers what big gaps can mean. Nothing here authenticates or grades a coin.
What weight and diameter tell you
A specification is a target the mint struck to. The U.S. Mint publishes weight, diameter, thickness, composition and edge treatment for its current circulating denominations — a dime is 2.268 grams and 17.91 millimetres, a quarter dollar 5.670 grams and 24.26 millimetres. Other mints publish equivalent tables for their issues. When your measurements land close to a candidate's published row, the identification gains support; when they land far off, the candidate needs rethinking. U.S. Mint: Coin Specifications
Read the numbers with their limits attached. Specifications describe newly struck coins — circulation wear removes metal, so a heavily worn coin reads under its spec weight while staying genuine. Mints also strike within manufacturing tolerances, so "a little off" is normal and "a lot off" is the flag. And a specification comparison is a check, not an authentication: a counterfeit can be engineered to match a published weight, which is why measurement feeds the wider verification sequence rather than replacing it.
The scale you need and how to use it
Coin weights are small, so resolution matters more than capacity. A pocket jeweller's scale reading to 0.01 grams is the right tool — a U.S. dime's 2.268-gram specification simply cannot be checked on a kitchen scale that rounds to the nearest gram. U.S. Mint: Coin Specifications
The routine is short:
- Set the scale on a stable, level surface away from drafts and let it settle.
- Calibrate if the scale supports it, or at minimum confirm it reads zero.
- Weigh a small container first and use the tare function, rather than balancing a bare coin on the platform edge.
- Weigh the coin, remove it, tare again and repeat once — two agreeing readings beat one dramatic one.
- Work over a soft surface, following the same handling habits as the care guide: edges, not faces, and no loose stacking.
Measuring diameter and thickness
Diameter is easier to get roughly right and harder to get precisely right than it looks. A clear ruler measures to about half a millimetre at best; a digital caliper reads to 0.01 millimetres and is the better tool if you measure coins often. Either way, the method is the same: measure across the widest part of the coin, through its centre — and if the coin is slightly out of round, take a second reading at another angle and record the larger.
Thickness matters less often but resolves some ambiguities: two issues can share a diameter while differing in thickness, and a coin that is suspiciously thick or thin for its candidate deserves a second look. Measure across the rim, where the coin is at its thickest, since the faces' relief makes a face-centre reading variable. The U.S. Mint's table lists thickness alongside weight and diameter for its current denominations — the same comparison discipline applies. U.S. Mint: Coin Specifications
Where the measurements come from
Widest point across the face, through the centre
Across the rim, not through the relief
Plain, reeded or lettered; lettered edges have orientation
Grams on a 0.01 g scale, measured twice
Editorial method summary; measurement is a clue, not authentication. Evidence: U.S. Mint: Coin Specifications; Royal Canadian Mint: Anatomy of a Coin.
Edge shape and orientation notes
The edge is a recorded feature, not just a boundary. The Royal Canadian Mint describes it as the coin's "third side", which may be plain or serrated — the serrated form is called reeding. Some issues carry lettering or symbols on the edge instead, so the honest record names what you see: plain, reeded, lettered or decorated. Royal Canadian Mint: Anatomy of a Coin
For lettered edges, orientation can matter. Lettering applied separately from the faces can land in either direction relative to the portrait — the Royal Mint Museum explains that on the UK's £2 coins the edge inscription is applied before striking, so its orientation relative to the portrait is random and is not an error. Record which way your edge lettering runs; just do not treat that orientation itself as a rarity flag without the issue's own documentation. Royal Mint Museum: Enquiries
One more orientation worth noting is how the two faces relate: some issues are struck so the reverse sits upright when the coin is flipped top-to-bottom, others when flipped side-to-side. Photographing both faces in the same session preserves this detail whether or not you record it deliberately.
Recording the numbers in a note
A good measurement record is one line, not a lab report: 8.04 g · 26.4 mm · reeded edge, kept beside the specification row it was compared with and the candidate issue it supports or complicates. Note the tool and its limits too — "kitchen ruler, ~0.5 mm" is more honest than a bare number, because the precision claim is part of the evidence.
That line slots straight into the upload flow: Coin Says Hi's optional note field can carry measured values, inscriptions and marks, so the provisional reading works with the same record you built. Try it with your coin photos — the numbers sharpen the description, and the result stays provisional regardless.
Questions people ask
My coin weighs less than the specification — is it fake?
Not by itself. Wear removes metal, so circulated coins routinely read under their as-struck spec; mints also strike within tolerances. A large gap with a confident identification is a reason to verify — the fakes guide covers the next checks — not proof on its own.
Do I need an expensive scale?
No — an inexpensive pocket scale reading to 0.01 grams covers coin work. What it needs is resolution, repeatability and a tare function; a kitchen scale that rounds to whole grams cannot resolve the differences between small denominations.
Why do two sources list different weights for the same coin?
Check which issue each source describes — design variants, different mints and different eras can share a denomination with different specifications. Then check the rounding: one source may quote the as-struck target while another describes a measured example. Compare like with like.
Should I weigh a coin in its holder?
A sealed holder adds its own mass, so record the result as "in holder" rather than presenting it as the coin's weight. Do not break a grading-service holder to get a number — the holder is part of the object's story, and the professional-roles guide explains what sealed certification means.
Does Coin Says Hi use my measurements?
It can — the optional note field accepts the weight, diameter and edge details you record, and a sharper description can sharpen the reading. The result remains provisional: measurements support a match, they do not authenticate one.
Sources and scope
The U.S. Mint's specifications table supplies the named U.S. weight, diameter, thickness and edge examples, scoped to its current circulating denominations; other mints publish equivalent tables for their own issues. The Royal Canadian Mint's anatomy page supports the edge and reeding definitions, and the Royal Mint Museum's enquiries page supports the £2 edge-orientation example. The measurement routine and record format are Coin Says Hi's editorial method — measurements are clues for comparison, not authentication, grading or a valuation. Sources last checked 2026-10-01.
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