Let's see. Back in the old days there were 4 British farthings in one pence (also called a penny) and 12 pence in a shilling, known affectionately as a bob. Twenty shillings made one pound, also called a sovereign and today in slang a quid, and 21 shillings made a guinea. To keep things interesting, two shillings were called a florin, and five shillings were called a crown. Coins were also issued in twopence, threepence, fourpence, and sixpence denominations, as well as double florins. A half crown was, of course, two and one-half shillings, or two shillings and a sixpence. When high resolution was needed, half farthings and one-third farthings came into play. This page addresses half farthings (1/1920th of a pound) with Queen Victoria on the front.
Here are some typical catalog values.
worn: $4 US dollars approximate catalog value
average circulated: $10
well preserved: $70
fully uncirculated: $200
1/2 farthings dated 1854 and 1856 are about twice as valuable as the figures above
Our favorite web site about farthings is (what else?) AboutFarthings.com.