Lot size calculator for prop firm traders

How to use it

1. Pick the instrument. The list covers forex majors, minors and exotics, gold, silver, stock indices, oil, bitcoin, ether and CME futures. 2. Choose your account currency and enter your balance. 3. Set your risk as a percentage of the balance or as a fixed amount. 4. Enter your stop loss. For forex it is in pips. For everything else it is a price distance: 5.00 on gold means a $5 move, 40 on an index means 40 points. Futures stops are in points too. 5. Check the contract size. It is filled in for you and can be changed, because one lot of gold, an index or a crypto pair is not the same on every platform. 6. Check the lot step. It is 0.01 lots by default and 1 contract for futures.

If the price is quoted in a currency other than your account's, the tool shows the exchange rate it uses. It starts with the European Central Bank's daily reference rate and its date. You can type today's rate instead.

What the result means

The tool works out what your stop costs on one lot: the stop distance, times the contract size, converted into your account currency. Your risk amount divided by that cost is the exact lot size.

Platforms only accept sizes in steps, so the tool rounds down to the lot step, never up. The loss at your stop can come in a little under your risk, but never over it. If even the smallest size would lose more than your risk, the tool says so and shows what the minimum size would risk.

The result also shows the units you would hold and the loss at the stop for the rounded size. To see what each pip or point is worth on its own, use the pip value calculator.

Worked example: gold

A $50,000 account risks 0.5% on gold (XAUUSD) with a stop $5.00 away from the entry. The contract size is 100 ounces a lot.

1. Risk amount: $50,000 times 0.5% is $250. 2. Cost of the stop on one lot: 5.00 times 100 ounces is $500. 3. Exact size: $250 divided by $500 is 0.50 lots. 4. Rounded down to the 0.01 step, the size stays 0.50 lots, and the loss at the stop is exactly $250.

If your platform's gold contract were 10 ounces instead, the stop would cost $50 a lot and the same risk would need 5.00 lots. That is why the contract size is visible and editable.

Common mistakes

• Trading a fixed lot. Using 1 lot on every trade means a 10 pip stop and a 40 pip stop risk very different amounts. Size each trade from its stop.
• Mixing up pips and points. Many platforms quote a fifth decimal on forex. Ten of those points make one pip, so a "200" stop on screen may be 20 pips.
• Assuming the contract size. Gold, indices and crypto lots differ between platforms. A wrong contract size gives a wrong lot size, sometimes by a factor of ten or more.
• Rounding up. 2.468 lots is 2.46, not 2.47. Rounding up puts the loss above the risk you chose.
• Ignoring costs. Spread, commission and slippage add to the loss when the stop is hit, especially around news.
• Confusing leverage with risk. Leverage decides the margin a trade needs, not what it loses at the stop. The margin and leverage calculator checks whether the position fits.

What to check at your firm

• Contract specifications. Check the contract size and the smallest lot step in your platform for every instrument you trade.
• Size limits. Some firms cap the lots you can open on one trade or in total.
• Risk rules. Some firms limit risk per trade or ask for a stop loss on every position.
• Daily loss and drawdown. The size that fits your risk should also fit today's room before a limit. The trade planner shows both on one screen, and the risk reward calculator checks the target.

Results depend on the inputs you enter, and firms' rules differ, so check your own firm's rules before you trade.

Running a prop firm? Read How to start a prop firm in 2026: tech, legal setup and a 90 day launch plan.