Everyday size guide
UK and US coin sizes compared
The UK 5p and US dime are almost identical in diameter: 18 mm and 17.91 mm respectively. The US nickel is wider than both at 21.21 mm.
Compare familiar UK and US coins below, with diameters, thicknesses and masses in one table. The main table covers modern everyday formats, with older versions explained separately. This compares physical size, not currency value.
Dime versus UK 5p: almost the same size
The UK 5p is just 0.09 mm wider than the US dime—a difference of about 0.5%.
Left: UK 5p coin18 mm diameter
Right: US dime17.91 mm diameter
The UK 5p measures 18 mm across its face, compared with 17.91 mm for the US dime.
That difference is difficult to see in a small illustration. The measurements are more useful than the pictures for telling their diameters apart.
US quarter versus UK 10p
The UK 10p is slightly wider than the US quarter: 24.5 mm compared with 24.26 mm.
Left: US quarter24.26 mm diameter
Right: UK 10p coin24.5 mm diameter
The difference is just 0.24 mm, making the UK 10p and US quarter another close match in diameter.
A coin's monetary value does not determine its size. The US dime, for example, is smaller than both the US penny and the US nickel.
UK and US coin dimensions
Diameter measures across a coin's face; thickness measures its depth from front to back. For the seven-sided 20p and 50p and twelve-sided £1, the table gives the maximum span across the coin.
| Coin | Diameter / maximum span | Thickness | Mass |
|---|---|---|---|
| US penny — Copper-plated zinc | 19.05 mm (0.750 in) | 1.52 mm (0.060 in) | 2.5 g |
| US nickel — Cupro-nickel | 21.21 mm (0.835 in) | 1.95 mm (0.077 in) | 5 g |
| US dime — Standard clad | 17.91 mm (0.705 in) | 1.35 mm (0.053 in) | 2.268 g |
| US quarter — Standard clad | 24.26 mm (0.955 in) | 1.75 mm (0.069 in) | 5.67 g |
| UK 1p coin — Copper-plated steel | 20.3 mm (0.799 in) | 1.65 mm (0.065 in) | 3.56 g |
| UK 2p coin — Copper-plated steel | 25.9 mm (1.020 in) | 2.03 mm (0.080 in) | 7.12 g |
| UK 5p coin — Smaller format, cupro-nickel reference | 18 mm (0.709 in) | 1.7 mm (0.067 in) (cupro-nickel reference; steel not established) | 3.25 g |
| UK 10p coin — Smaller format, cupro-nickel reference | 24.5 mm (0.965 in) | 1.85 mm (0.073 in) (cupro-nickel reference; steel not established) | 6.5 g |
| UK 20p coin — Cupro-nickel, seven-sided | 21.4 mm (0.843 in) | 1.7 mm (0.067 in) | 5 g |
| UK 50p coin — Smaller format, cupro-nickel | 27.3 mm (1.075 in) | 1.78 mm (0.070 in) | 8 g |
| £1 coin — Twelve-sided, bimetallic | 23.43 mm (0.922 in) | 2.8 mm (0.110 in) | 8.75 g |
| UK £2 coin — Bimetallic | 28.4 mm (1.118 in) | 2.5 mm (0.098 in) | 12 g |
Inch conversions use 1 inch = 25.4 mm. “Clad” describes a coin made with layers of different metals; “bimetallic” here describes the £2 coin's outer ring and inner disc.
A wider coin is not necessarily heavier: thickness and material matter too. Open any coin's name for its illustration, measurement notes and sources.
Same denomination, different material
Some coins kept the same diameter when their material changed, but their thickness or mass changed.
For UK pennies, the published thicknesses are:
- 1p: 1.52 mm for bronze and 1.65 mm for copper-plated steel.
- 2p: 1.85 mm for bronze and 2.03 mm for copper-plated steel.
The main table uses the copper-plated steel versions. The Royal Mint records both 2p alloys in 1998: material labels are more reliable than a simple year cutoff.
The smaller UK 5p and 10p have also been made in cupro-nickel and nickel-plated steel. The table explicitly uses cupro-nickel reference thicknesses: 1.7 mm and 1.85 mm. The Mint's general pages list those thicknesses without splitting materials; secondary references report steel thicknesses of 1.89 mm and 2.05 mm. We have not established those as official steel specifications and do not assign them to the default records. See the 5p material notes and 10p material notes before comparing a steel coin.
The material change in January 2012 was separate from the earlier diameter reductions. The Royal Mint — cupro-nickel replacement programme (archived) confirms that cupro-nickel coins remained legal tender during the recovery programme.
The US penny entry describes the copper-plated zinc format, while the dime and quarter entries describe standard clad coins. Earlier copper-alloy pennies and silver dimes or quarters should not automatically be assigned the masses in this table.
Older coin sizes
An older coin can have the same face value as a modern one but a different physical size. The UK introduced smaller 5p, 10p and 50p coins in 1990, 1992 and 1997 respectively.
| Coin | Older format | Newer format | Newer format introduced |
|---|---|---|---|
| UK 5p coin | 23.59 mm | 18 mm | 1990 |
| UK 10p coin | 28.5 mm | 24.5 mm | 1992 |
| UK 50p coin | 30 mm | 27.3 mm | 1997 |
| £1 coin | 22.5 mm, round | 23.43 mm, twelve-sided | 2017 |
These years mark the introduction of the newer formats, not necessarily the withdrawal of the older ones. The Royal Mint dates withdrawal of the larger 5p to 1990, the larger 10p to 1993 and the larger 50p to 1998. These are not last-minted dates.
Old and new pound
The £1 changed in the opposite direction to the other three: the twelve-sided pound is wider, but also thinner and lighter, than its round predecessor.
| £1 version | Published thickness | Mass |
|---|---|---|
| Twelve-sided | 2.8 mm (0.110 in) | 8.75 g |
| Older round pound | 3.15 mm (0.124 in) | 9.5 g |
The twelve-sided pound entered circulation on 28 March 2017; the round pound lost legal tender status on 15 October 2017. Use the older measurements when comparing an older-format coin. A different portrait or reverse design alone does not necessarily mean a coin has different dimensions.
Sources and coin versions
The measurements come from published specifications for the formats identified here. These are nominal specifications; an individual coin may measure differently because of wear or how it is measured.
- US Mint — circulating coin specifications
- Royal Mint — 1p specifications
- Royal Mint — 2p specifications
- Royal Mint — 5p specifications and format history
- Royal Mint — 10p specifications and format history
- Royal Mint — 20p specifications
- Royal Mint — 50p specifications and format history
- Royal Mint — £1 coin specifications
- Royal Mint — bimetallic £2 specifications
- US Mint: the history of coin materials
- Royal Mint: the twelve-sided pound
The US Mint pages could not be retrieved directly during this review (HTTP 403). Existing diameter and mass records were retained; thicknesses were corroborated with US penny — composition and dimensions reference and CoinNews — US circulating coin specifications, not claimed as freshly checked on the Mint's site.
Original 5p, 10p and 50p diameters are corroborated by UK 5p — material-specific and historical dimensions reference, UK 10p — material-specific and historical dimensions reference and UK 50p — historical dimensions reference; introduction and withdrawal dates use the denomination-specific Mint pages above. The Royal Mint — £1 coin specifications supports both pound formats.
Check the format when comparing a coin you own. Different designs can share the same measurements, while changes in material or shape can affect thickness, diameter or mass. Collector versions are not automatically covered by the main table.
The illustrations help identify the coins and compare their marked dimensions. They are not exact reproductions of mint designs, and a face-on illustration does not show thickness.
For another everyday comparison, explore dry seed sizes from poppy to chickpea.
You can also try estimating and comparing sizes or read how our scale comparisons work.