The arithmetic behind a gold lot size
XAUUSD's contract size is different from a currency pair's, and that difference is the whole reason gold position sizing trips people up. A typical 1.00 lot of gold is 100 troy ounces, so a $1.00 move in gold's own price is worth $100 per lot — not the $10-per-pip-per-lot most traders are used to from EURUSD or GBPUSD. This calculator turns that fact into three steps: risk dollars = balance × risk% ÷ 100; loss per 1.00 lot = stop distance (in gold's own dollars) × $100; and the raw lot size = risk dollars ÷ loss per lot. At the defaults — a $10,000 balance, 1% risk, and a $5.00 stop — that's $100.00 risked, $500.00 lost per 1.00 lot at that stop, and 0.2 lots unrounded, which stays exactly 0.20 after flooring. Double the risk to 2% with the same $5.00 stop and the position size doubles to 0.40 lots; keep the risk at 1% but widen the stop to $10.00 instead and it halves back to 0.10 lots — the same balance and the same dollars at risk, sized differently because the stop moved. That's the whole relationship: bigger risk widens the position, a wider stop shrinks it, and the $100-per-lot gold contract is the multiplier connecting the two.
Why the calculator floors, never rounds
A $5,000 balance risking 2% with an $8.00 stop needs $100.00 of risk against $800.00 of loss per 1.00 lot — an unrounded lot size of exactly 0.125, sitting precisely between the broker's 0.12 and 0.13 steps. Round that up to 0.13 lots and the real dollar risk becomes $104 — over the $100 the trader actually typed in. Round down to 0.12 and real risk is $96 — under it. Only one of those two directions can't silently break the number a trader set, so this calculator always floors to the nearest 0.01 lot and never rounds up, even when the unrounded value sits a hair's-width from the next step. The same floor can also reach zero: a $1,000 balance risking 1% with a $20.00 stop needs $10.00 of risk against $2,000.00 of loss per lot — an unrounded 0.005 lots, which floors to 0.00. Rather than pretend a fraction of the broker's smallest step is tradeable, the calculator says so plainly: the stop is too wide for that balance at that risk percent. The honest fix is a smaller stop, a bigger account, or accepting the trade doesn't fit at this size — not a lot size that quietly risks more than intended.
What this doesn't include
Every number above assumes the typical 100 oz XAUUSD contract — the standard most retail gold CFDs and forex-style gold pairs use, though it isn't universal. Some brokers offer mini or micro gold contracts, or price gold differently on cent or nano accounts, so the $100-per-lot multiplier this calculator uses may not match your own broker's specification exactly — check your broker's contract page before sizing a real position from these numbers. This is also pure position-sizing arithmetic on the balance, risk percent, and stop distance you enter — it doesn't add spread, commission, swap, or slippage, all of which add real cost on top of whatever this calculator reports. Treat the output as the starting point for a position size, not the final word on what a trade will actually cost.