Position size calculator
Lot size is the one variable still free after the stop is placed, and it is where accounts are actually lost. This computes it from your balance, the risk you stake and the stop distance — with the round trip included, because the spread and commission come out of the same stake, and the published formula that ignores them hands you a position that loses more than you agreed to every time the stop is hit.
The formula, and the cost it leaves out
The published version reads: risk divided by stop distance times pip value. It is not wrong as arithmetic; it is wrong as accounting. The moment a position opens, the spread has been crossed and the commission charged, and both came out of the same stake the formula was allocating. Size to the textbook figure and a stopped trade loses the stated risk plus the round trip — the stake you agreed was the one number under your control, exceeded on every loss by construction.
The gap is not academic at the stop distances traders actually use. The round trip is a fixed toll per lot, so the tighter the stop, the larger the share of the stake it eats: at a wide stop the two figures nearly agree, at a scalper's stop the textbook size can be oversized by a double-digit percentage. The panel above prints both figures and the gap, so the difference is a number rather than an argument.
Quote currency, and why there is a rate field
Contract size times pip increment is denominated in the instrument's quote currency — dollars on EUR/USD, yen on GBP/JPY. If your account is not held in that currency, every figure above needs converting at a rate this page does not know and will not invent. That is what the quote-to-account field is: on a dollar account trading a dollar-quoted pair it stays at 1 and the figures are exact; anywhere else, enter your broker's rate and the conversion is yours rather than an assumption smuggled in as a fact.
Lot size calculator, position size calculator — one arithmetic
The two names circulate as if they were different tools, and they are not: a lot size calculator answers in lots, a position size calculator answers in whatever unit the account trades, and the arithmetic underneath is identical. This page prints both — lots as the headline figure, units beside it — so whichever name brought you here, the number you leave with is the same one, costs included. The only real difference worth knowing is the one no name advertises: whether the round trip was subtracted before the size was computed, and here it is.
What this does not do
It does not know whether the trade is any good. Sizing controls what a losing trade costs; it says nothing about how often trades lose, and no position size converts a negative expectancy into a positive one. The forward question — how likely a given sizing is to run an account into a floor it cannot come back from — is the risk of ruin calculator, and it needs your win rate, which this page deliberately never asks for.
The presets are starting points, not facts about your account: contract sizes, pip conventions, spreads and margin requirements all vary by broker, and where a figure here disagrees with your account statement, your statement is right. The margin row is indicative for the same reason, and appears only when you supply a price.
The stake this sizes against usually lives inside a larger allowance: the distance to a trailing floor is the trailing drawdown calculator, and the price at which the broker closes the position for you is the margin and stop-out calculator. The cost mechanics above are defined at execution cost and slippage — and slippage is the reason the loss at your stop is a floor rather than a ceiling. What that stake buys on the other side — the target measured against the stop it risks — is the risk reward ratio calculator, and the money a closed trade actually lands once the round trip is taken out is the forex profit calculator. The full list is under calculators. The live version of this arithmetic — every open position folded into one exposure, the largest still-permissible size recomputed on each fill — is the Prop-Evaluee Risk Guardian. And when the inputs cannot support an answer, the panel above refuses and says why rather than rendering a zero — why an instrument refuses to answer is that design, written down.