Position size is the quantity you choose for a trade. It is one of the few things fully under your control, and it decides how much a given price move affects your account. This guide explains how to calculate position size in forex using a simple worksheet, so that the quantity follows from a limit you set in advance rather than from habit or guesswork.
This article is educational information, not financial, investment or legal advice. It draws on official and provider documentation rather than personal trading results. No broker or strategy is endorsed. Disclosure: forexbrokers.net may earn a commission if you open an account through some links on this site; that does not change what we explain here. Forex trading can cause substantial losses.
Why position size comes first
Many beginners choose a quantity first and think about risk afterwards. That order is backwards. If the quantity is chosen by habit, the amount at risk on each trade becomes whatever that habit happens to produce. Working out the size from a limit you have already chosen reverses this, so the limit drives the quantity instead of the other way around.
Leverage makes this more important. ASIC’s Moneysmart forex guide explains the risks of leveraged currency trading for retail investors. Because leverage allows a large position on a smaller deposit, an unplanned quantity can expose far more of an account than intended.
What a worksheet can and cannot do
A position size worksheet helps you plan. It cannot guarantee that a loss will stop where you planned, because orders may not always be filled at the exact level you chose. Treat the result as a planning figure and read your provider’s execution terms to understand how its orders behave.
The inputs you need
Before you can calculate position size in forex, gather four inputs. Each one comes from your own decision or from your provider’s documents, not from a general rule.
Input 1: Your account currency and equity
Note the currency your account is held in and its current equity. Equity reflects open positions, so use the figure your platform shows rather than the amount you originally deposited.
Input 2: Your planned maximum loss for this trade
Decide in advance the most you are prepared to lose on this single idea, written as an amount in your account currency. This is a personal decision. There is no figure that suits everyone, and this guide does not suggest one.
Input 3: Your stop distance
Decide where you would exit if the trade moves against you, and measure the distance from your planned entry in pips. Check the instrument specification to confirm where the pip decimal sits for that pair before you count.
Input 4: The value of one pip per unit
Work out what one pip is worth for one unit of the base currency, in your account currency. Britannica Money’s introduction to retail forex explains that pip value depends on your currency and the size of the position, which is why you calculate it per unit first and scale it afterwards.
How to calculate position size in forex: the formula
With the four inputs in hand, the calculation follows one relationship:
Position size in units = planned maximum loss ÷ (stop distance in pips × pip value per unit)
The answer is a number of units of the base currency. If your platform uses lots, divide by the contract size in the instrument specification to convert units into lots. Then round down to the nearest size the platform accepts, so the rounded size does not exceed your planned limit.
Why round down
Platforms only accept quantities in fixed steps. Rounding up would place a little more at risk than you planned. Rounding down keeps the planned figure as a ceiling. If rounding down leaves a size below the platform’s minimum, the trade as planned does not fit your limit, and that is a useful result in itself.
A worksheet you can copy
Write the worksheet as a short table or a set of lines in your journal. Fill in each line before you open the order ticket.
- Account currency
- Current equity
- Planned maximum loss for this trade
- Pair, written as base and quote
- Planned entry level
- Planned stop level
- Stop distance in pips
- Pip value per unit, in account currency
- Position size in units, from the formula
- Contract size from the specification
- Position size in lots, rounded down to the allowed step
- Platform’s margin preview for this size
The last line connects sizing to margin. A size that fits your loss limit still needs enough free margin to open. If the preview shows a requirement you are not comfortable with, reduce the size or reconsider the trade.
Checking your worksheet against the platform
Once the worksheet is complete, open the order ticket, enter the size and stop level, and stop before sending. Many platforms show an estimated value per pip or an estimated loss at the stop. Compare that estimate with your worksheet.
If the two differ, find out why before trading. Common reasons include a different contract size from the one you assumed, a quantity field measured in units rather than lots, or a currency conversion step you missed. The MetaTrader 5 trading principles guide is a useful reference for how orders, deals and positions relate, and your provider’s help pages explain how its own figures are calculated.
Include costs in your plan
The formula above measures price movement only. Spreads, commissions and any financing charges add to the result. Read the charge schedule for your account and decide whether to leave room for those costs inside your planned maximum loss. Our fees and accounts guides explain how to record each cost.
When the worksheet says no
Sometimes the calculation produces a size that is too small to trade, or a margin requirement that is too large. Both outcomes are the worksheet doing its job. A very small size usually means the stop is far from the entry compared with your limit. A large margin requirement usually means the position is large compared with your equity.
In either case, the choices are to adjust the plan or skip the trade. Moving the stop closer only to make the numbers fit changes the idea itself, so write down why you are doing it if you decide to. Increasing your limit to make a trade fit defeats the purpose of setting it in advance.
Several positions at once
If you hold more than one position, each one has its own planned loss, and those amounts can add up. Positions in related currencies may also move together. Before opening another position, add up the planned losses of everything already open and ask whether the total still fits what you are prepared to lose.
Your provider’s terms decide how margin is shared across positions. Read those terms so you understand how one position’s result can affect the free margin available to others.
Common position-sizing mistakes
- Choosing size before the stop. Decide the stop first, then calculate the size.
- Using the deposit instead of equity. Equity reflects open positions.
- Forgetting the conversion step. Pip value must be in your account currency.
- Rounding up. Round down so the planned limit stays a ceiling.
- Ignoring costs. Spreads and commissions add to the price-based result.
- Treating the plan as guaranteed. Execution can differ from the planned level.
Before you trade at all
Position sizing only matters if the account itself is with a legitimate provider. The CFTC’s advisory on eight things to know before trading forex recommends checking registration and disciplinary history before opening an account. In the US, the NFA’s BASIC database holds registration information for retail forex firms. Our broker safety guides explain how to match a provider to an official record.
FAQ
What is the formula for position size in forex?
Position size in units equals your planned maximum loss divided by the stop distance in pips multiplied by the pip value per unit.
Should I round the result up or down?
Down, to the nearest size your platform accepts, so you stay within your planned limit.
Does correct sizing prevent losses?
No. It helps you plan the size of a loss, but it does not prevent losses and execution may differ from the planned level.
Risk warning: Forex and CFD trading uses leverage and can result in substantial losses. Past performance does not indicate future results. Nothing here is a recommendation to buy or sell any currency. If the implications are unclear, seek independent qualified advice.
