Lot size calculator
The same arithmetic as position sizing, asked the other way round, and with the one input that actually differs between instruments made explicit.
Leave the exchange rate at 1 if your account is in the currency the instrument is priced in. Otherwise enter how many units of that currency one unit of your account currency buys. Contract size is what one lot controls: 100 ounces for XAUUSD, 100,000 units for a standard forex lot, usually 1 for a cash index. Stop distance is in the units the instrument is priced in. Check both against your own platform.
Free, and nothing is stored. Check every figure against your own platform before you trade on it. Nothing here is advice, and trading carries risk.
Most lot size calculators quietly assume you are trading a currency pair. Then somebody uses one for gold or the Nasdaq and the answer is out by a factor of a thousand.
The thing that differs is contract size: what one lot actually controls. 100 ounces for XAUUSD. 100,000 units for a standard forex lot. Usually 1 for a cash index. It is an input here rather than an assumption.
The arithmetic: loss per lot if stopped = stop distance × contract size. Then position size = risk amount ÷ loss per lot.
Worked through on gold, with a dollar account: $10,000 at 1% is $100 of risk. A $5 stop with 100 ounces per lot loses $500 per lot, so the position is 0.2 lots. With a sterling account the £100 of risk has to be converted into dollars first, which is what the exchange rate field is for.
Stop distance is in whatever units the instrument is priced in, so dollars for gold and points for an index. Both inputs are worth checking against your own platform rather than assuming.
Typical contract sizes, and every one of these varies by broker: a standard forex lot is 100,000 units of the base currency; XAUUSD is 100 troy ounces; XAGUSD is 5,000 ounces; cash index CFDs such as US30, NAS100 and the FTSE are usually 1 per point per lot, though some brokers use 10 or 20; futures contracts have their own specification per contract and do not use lots at all.
That variation is the whole reason contract size is a field here rather than a hidden constant. A US30 lot size calculator and a gold lot size calculator are the same arithmetic with a different number in one box, and a tool that hides that number is the reason people size trades wrongly when they move between instruments.
The same applies whichever platform you use. MetaTrader shows contract size in the symbol specification, and it is worth reading once for each instrument you actually trade rather than assuming the default carries over.
The ones people actually ask.
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