Lot Size Calculator for MT5: How to Size Every Trade by Risk
A lot size calculator tells you how many lots to trade so that, if your stop loss is hit, you lose exactly the amount you decided to risk - no more, no less.
Most new traders do it the other way round. They pick a lot size that "feels right", then place the stop wherever it fits. The result is a different risk on every trade: $20 on one, $90 on the next, and one bad day that wipes out a week of good ones.
This guide shows how to calculate lot size by hand, why pip value matters, and how to let MT5 do it for you on the chart.
What a Lot Is: Standard, Mini and Micro
In forex, a lot is a fixed number of units of the base currency:
| Lot | Units | Pip value on EURUSD (USD account) |
|---|---|---|
| 1.00 (standard) | 100,000 | about $10 |
| 0.10 (mini) | 10,000 | about $1 |
| 0.01 (micro) | 1,000 | about $0.10 |
The lot size is the volume you type in MT5. It is the only number that turns "my stop is 25 pips away" into "I will lose $X".
Pip Value: The Missing Piece
Pip value is how much money one pip is worth for one lot. On pairs quoted in USD (EURUSD, GBPUSD, AUDUSD) it is about $10 per standard lot for a USD account. On other pairs it changes with price - on USDJPY, for example, it is lower and moves as the yen rate moves.
This is why a fixed lot is not a fixed risk. The same 0.50 lots and the same 20-pip stop cost different money on EURUSD, USDJPY and gold.
How to Calculate Lot Size (the Formula)
You need three numbers: your account balance, the percentage you want to risk, and your stop loss distance.
Lot size = (Balance × Risk %) ÷ (Stop loss in pips × Pip value per lot)
Example 1 - EURUSD:
- Balance: $10,000. Risk: 1% = $100.
- Stop loss: 25 pips. Pip value: $10 per lot.
- Lot size = 100 ÷ (25 × 10) = 0.40 lots.
Example 2 - same account, wider stop:
- Stop loss: 50 pips.
- Lot size = 100 ÷ (50 × 10) = 0.20 lots.
The risk stays $100 in both trades. A wider stop simply means a smaller position. That is the whole point of a position size calculator: the stop goes where the chart says it should, and the lot size adjusts.
Position Size Calculator vs Doing It by Hand
The formula is simple, but doing it by hand before every trade has three problems:
- It's slow. By the time you have measured the stop, looked up the pip value and done the division, price has moved.
- Pip value isn't always $10. Crosses, JPY pairs, gold and indices each need their own number.
- Brokers round lots. Most allow steps of 0.01 lots, some 0.1 or even 1. Your 0.437 has to become a number the broker accepts.
An online calculator fixes the maths but not the speed: you still copy prices from the chart into a website, then back into MT5.
Using a Lot Size Calculator Inside the MT5 Chart
The ATC Position Tool and Trade Manager MT5 (also part of the All In One Trade Management Panel MT5) puts the calculator on the chart:
- Place a long or short position on the chart and drag the stop loss and take profit lines where you want them.
- Choose Percent risk (of balance), a Fixed Lot, or a saved Preset (for example A+ = 2%, B = 1%, C = 0.5%).
- The lot size, the money at risk and the R:R update live as you drag.
- Lots are rounded to your broker's lot step and kept within its minimum and maximum.
- The tool reads the symbol's real tick value from your broker, so the same steps work on forex, gold, indices and crypto.
Once the lines are right, send the trade at market, as a pending order, or save it as a plan for later.
FAQ
What is 0.01 lot?
0.01 lot is a micro lot: 1,000 units of the base currency. On EURUSD it is worth about $0.10 per pip for a USD account. It is the smallest size most brokers allow.
What lot size should I use for a $100 account?
At 1% risk you can lose $1 per trade. With a 20-pip stop on EURUSD that is 0.005 lots - below the 0.01 minimum. So with $100 you either risk 2% at 0.01 lots, use a tighter stop, or use a cent account. A calculator shows this before you enter, not after.
What is the difference between standard, mini and micro lots?
Standard = 1.00 lot (100,000 units), mini = 0.10 (10,000), micro = 0.01 (1,000). They change your pip value by the same factor: $10, $1 and $0.10 per pip on EURUSD.
Is a lot size calculator the same as a position size calculator?
Yes. Both find the trade volume that matches your chosen risk and stop distance.
Read next
- Tomorrow: Fixed Lot or Percent Risk? How Much to Risk per Trade
- Try the panel free on a demo account: free trial
