An ordinary 5 pence (5p) coin is worth 1/20 of a pound sterling (£1), the basic currency of the United Kingdom. This has been true since the decimalisation of that country's currency in the early 1970s, when 1 pound became equal to 100 pence. Previously there had been no such denomination in British coinage.
The Smaller 5p
With a diameter of 18mm---which is slightly larger than the U.S. dime---the current 5 pence coin, in production since 1990, is a smaller version of the one introduced at the time of decimalisation. The older coins are no longer legal tender and thus have no value, though some may be of value to coin collectors.
The 5p coin is 75 per cent copper and 25 per cent nickel, and contains no precious metal such as silver. At a weight of 3.25 grams, the intrinsic value of the coin's metal is very small, considerably less than 5 pence.
As Legal Tender
According to the United Kingdom's Royal Mint, 5p coins are "legal tender for amounts up to £5," or 100 coins used at the same time to buy something.
As a relatively new British coin, the collectable market for 5p coins is limited. However, uncirculated (no wear whatsoever) examples of the some of the earliest years may fetch a few pounds, as do more recent uncirculated 5p coins taken from collector sets originally sold by the Royal Mint. Proof 5p coins---highly polished and double-struck during minting---also command a few pounds, but no more than about £10.
As Foreign Exchange
Banks rarely exchange one country's coins for another, but there are specialists who do, though the exchange rate will not be as favourable as when exchanging banknotes or other, larger forms of currency. In theory at least, a 5p coin is worth 1/20 of the current exchange rate for a pound sterling. (For example, at £1 = U.S. 90p, then 5p would equal U.S. 7.5¢.)