Some National Currencies
Note that this is just a rough overview of which countries used which currencies, and what sizes they came in. Due to the mixture of sizes and materials throughout the period, especially a mixture of coins and notes, I am making very little attempt to distinguish which is which. If you are going to refer to a specific item in your story, such as a penny coin, be certain that it existed in that currency at the time.
Also, beware of what inflation calculators tell you. Buying power and goods to be bought are not necessarily comparable over time. For instance, the BLS inflation calculator tells us that a dollar of 1940 money is equal to $15.60 in 2010 money. However, some items were much cheaper in 1940, some were much more expensive, and some were unattainable at any price. Nobody in 1940 would have been able to able to buy a digital watch. Even the out-of-season fruits and vegetables that populate our produce departments would have been far more expensive to ship in than they are today. Labor, on the other hand, cost less than it does today, perhaps due to less of a need for those laborers to purchase digital watches. Again, checking prices of the time (especially from primary sources) can be invaluable.
I should also note that this is preliminary, and very much a work in progress. In all probability, this information is incomplete or inaccurate. Don't rely solely on it. Especially not if you're planning any time travel.
The US has always had a decimal money system. The exact coins have varied somewhat, as have which were available in notes versus coins, especially in the old gold coins. For temporal conversion, you can use the BLS Inflation Calculator.
British coin abbreviations come from the old Roman terms libra (pound), solidus (shilling), and denarius (penny), hence £, s, and d, often abbreviated further into £/s/d, as in 3/5/2, meaning 3 pounds, 5 shillings, and twopence. In 1971, British currency was converted to a decimal system. For temporal conversion, you can use the National Archives calculator.
Additional British combinations and slang
|Half-crown||2 shillings and sixpence|
|Guinea||1 pound and 1 shilling|
|Centime coins||1, 5, 10, 25, 50 centimes|
|Franc coins||1, 2 francs|
|Kopek coins||1, 2, 3, 5, 10, 15, 20, 50 kopeks|
|Ruble coins||1, 2, 5, 10 rubles|
|Ruble notes||1, 3, 4, 10, 25, 50, 100, 200, 500, 1000 rubles|
Note that P.O.W.s were issued scrip (Lagergeld) that was not actually legal tender.
|Pfennig coins||1, 2, 5, 10, 50 reichspfennigs|
|Mark coins||1, 2, 5 reichsmarks|
|Mark notes||5, 10, 20, 50, 100, 1000 reichsmarks|