"As many UK coins do not have a denomination on them, especially prior to the 20th century, the following gives an index by diameter and weight for Milled coins only. Bear in mind that coins from the 18th Century and earlier show significant variations both in diameter and weight from issue to issue. Hammered coins show far too much variation for them to be indexed in this way.

Milled coins are those produced on a machine press, and have a regular size. This process became standard around the time of Charles II in the middle of the 17th century. Prior to that coins were made by hand hammering, and as there was no collar the size of the coin was irregular. The term milled is also applied to the lines on the edge of the machine-made coins which were introduced to prevent the practice of clipping silver or gold from round the edge.

The term 'Early' as used in the list below generally means pre-1816. Such coins show variations around the figure given

Copper or Bronze Coins:

• 13.5 mm 1.2 g Quarter Farthing
• 15.0 mm 1.0 g Bronze Third Farthing
• 16.0 mm 1.5 g Copper Third Farthing
• 17.1 mm 1.8 g Decimal Half Penny
• 18.0 mm 2.4 g Copper Half Farthing
• 20.0 mm 2.8 g Bronze Farthing
• 20.3 mm 3.6 g Decimal Penny
• 22.0 mm 4.7 g Copper Farthing
• 22.0 mm 5.0 g Early Copper Farthing
• 23.0 mm 6.0 g 1799 Farthing
• 25.0 mm 5.7 g Bronze Halfpenny
• 25.9 mm 7.1 g Decimal Two Pence
• 28.0 mm 9.3 g Copper Halfpenny
• 29.0 mm 10.0 g Early Copper Halfpenny
• 30.5 mm 12.5 g 1799 Copper Halfpenny
• 31.0 mm 9.4 g Bronze Penny
• 34.0 mm 18.8 g Copper Penny
• 36.0 mm 28.3 g 1797 Copper Penny
• 41.0 mm 57 g 1797 Copper Two Pence
  

• Brass
  • 21.0 mm 6.8 g Three Pence
  • 22.5 mm 9.5 g Decimal One Pound
  • 28.4 mm 16.0 g Decimal Two Pounds (Commemorative)
• Brass/Cupronickel Bimetallic
  • 28.4 mm 12.0 g Decimal Two Pounds (Circulation issue)
• Silver (or Cupronickel)
  • 11.0 mm 0.5 g Maundy Penny
  • 12.0 mm 0.5 g Early Maundy Penny
  • 12.0 mm 0.7 g The Penny-Halfpeny
  • 13.0 mm 0.9 g Maundy Two Pence
  • 14.0 mm 1.0 g Early Maundy Two Pence
  • 16.0 mm 1.4 g Three Pence
  • 16.0 mm 1.9 g Four Pence or Groat
  • 17.0 mm 1.5 g Early Three Pence
  • 18.0 mm 1.9 g Maundy Four Pence
  • 18.0 mm 3.3 g Decimal Five Pence
  • 19.0 mm 2.0 g Early Maundy Four Pence
  • 19.0 mm 2.8 g Sixpence
  • 21.0 mm 3.0 g Early Sixpence
  • 21.4 mm 5.0 g Decimal Twenty Pence
  • 24.0 mm 5.7 g Shilling
  • 24.0 mm 5.7 g Decimal Five Pence (large)
  • 24.5 mm 6.5 g Decimal Five Pence (small)
  • 25.5 mm 6.0 g Early Shilling
  • 27.0 mm 7.4 g 18 pence
  • 27.3 mm 8.0 g Decimal Fifty Pence (small)
  • 28.0 mm 11.3 g 1849 Godless Florin
  • 28.5 mm 11.3 g The Florin or Two Shillings
  • 28.5 mm 11.3 g Decimal Two Pence (large)
  • 29.5 mm 11.3 g Jubilee Florin
  • 30.0 mm 11.3 g Gothic Florin
  • 30.0 mm 13.5 g Decimal Fifty Pence (large)
  • 32.0 mm 14.1 g Half Crown
  • 34.0 mm 15.0 g Early Half Crown
  • 35.0 mm 15.0 g Three Shillings
  • 36.0 mm 22.6 g Four Shillings
  • 39.0 mm 28.3 g Five Shillings or Crown (date before 1970)
  • 39.0 mm 28.3 g Decimal 25 pence
  • 39.0 mm 28.3 g Decimal 5 pounds
  • 39.0 mm 30.0 g Early five shillings (or Crown)
• Gold
  • 16.0 mm 2.1 g Quarter Guinea
  • 17.0 mm 2.8 g Third Guinea
  • 19.0 mm 4.0 g Half Sovereign
  • 20.0 mm 4.2 g Half Guinea
  • 22.0 mm 8.0 g Sovereign
  • 25.0 mm 8.4 g One Guinea
  • 28.0 mm 16.0 g Two Pounds
  • 31.5 mm 16.8 g Two Guineas
  • 37.0 mm 40.0 g Five Pounds
  • 37.0 mm 41.9 g Five Guineas
  • 38.0 mm 39.0 g 1826 or 1839 Five Pounds"
    

I hope this information was helpful and benefited your knowledge on the subject.