Position Size Calculator
Quickly compute position size with accurate formulas. See amortization schedules, growth projections, and side-by-side comparisons.
Calculator
Adjust values & calculateProfit Targets (Risk Multiples)
Formula
Divide your dollar risk amount (account × risk percentage) by the price difference between entry and stop loss. This gives you the exact number of shares or units where your maximum loss equals your intended risk. Round down to whole shares for stocks.
Last reviewed: December 2025
Worked Examples
Example 1: Stock Position Sizing
Example 2: Crypto Position Sizing
Background & Theory
The Position Size Calculator applies the following established principles and formulas. Foreign exchange markets facilitate the conversion of one currency into another and serve as the largest and most liquid financial markets in the world, with daily turnover exceeding seven trillion US dollars. Exchange rates are quoted as currency pairs, expressing the price of one unit of a base currency in terms of a quote currency. For example, a EUR/USD rate of 1.0850 means one euro buys 1.0850 US dollars. The smallest standardized price movement in most pairs is the pip, typically the fourth decimal place, with a value of 0.0001 per unit for USD-denominated pairs. The bid price is the rate at which a dealer will buy the base currency, while the ask price is the rate at which it will sell. The spread between bid and ask represents the dealer's compensation and varies with liquidity and volatility. Leverage amplifies both gains and losses by allowing traders to control positions larger than their deposited margin. A 100:1 leverage ratio means a one-percent adverse move eliminates the entire margin, making position sizing and risk management critical. Two parity conditions from international economics anchor exchange rate theory. Purchasing Power Parity (PPP) holds that exchange rates should adjust over time so that identical goods trade at equivalent prices across countries: S = P_d / P_f, where S is the spot rate and P_d and P_f are domestic and foreign price levels. PPP performs well over long horizons but poorly in the short run due to trade barriers, non-tradable goods, and capital flows. Covered Interest Rate Parity (CIRP) is a near-arbitrage condition stating that forward exchange rate premiums or discounts exactly offset interest rate differentials between two currencies: F/S = (1 + r_d) / (1 + r_f). Deviations from CIRP create riskless arbitrage opportunities that traders rapidly eliminate. Uncovered Interest Rate Parity posits that high-yielding currencies should depreciate to offset their interest advantage, though empirical evidence is mixed and the carry trade — borrowing in low-rate currencies to invest in high-rate ones — has generated persistent returns.
History
The history behind the Position Size Calculator traces back through the following developments. For much of the nineteenth century and early twentieth century, the international monetary system operated under the classical gold standard, under which each participating currency was fixed to a defined weight of gold, making bilateral exchange rates effectively constant. The system provided price stability and facilitated global trade but constrained governments' ability to respond to economic downturns. World War One shattered the gold standard as nations suspended convertibility to finance wartime expenditures. The interwar period saw attempts to restore gold convertibility, most notably the British return to the gold standard in 1925 at the pre-war parity, a decision criticized by John Maynard Keynes as deflationary. The Great Depression forced widespread currency devaluations and the effective collapse of the international gold standard by the early 1930s. The Bretton Woods Conference of July 1944 established a new order in which member currencies were pegged to the US dollar, while the dollar alone was convertible into gold at 35 dollars per troy ounce. The International Monetary Fund and World Bank were created at the same conference to oversee the system. Bretton Woods delivered exchange rate stability during the postwar growth era but came under strain as US deficits and European dollar accumulation outpaced American gold reserves. On August 15, 1971, President Nixon announced the suspension of dollar-gold convertibility — the so-called Nixon Shock — effectively ending the Bretton Woods system. By 1973, major currencies had transitioned to floating exchange rates determined by market supply and demand, a regime that has persisted. On September 16, 1992, hedge fund manager George Soros shorted the British pound against the European Exchange Rate Mechanism constraints, forcing the UK's withdrawal in what became known as Black Wednesday. Electronic trading platforms emerged in the 1990s and 2000s, replacing voice-brokered interbank markets and dramatically reducing transaction costs for institutional and retail participants alike.
Frequently Asked Questions
Sources & References
Formula
Position Size = (Account Balance × Risk %) / |Entry Price - Stop Loss Price|
Divide your dollar risk amount (account × risk percentage) by the price difference between entry and stop loss. This gives you the exact number of shares or units where your maximum loss equals your intended risk. Round down to whole shares for stocks.
Worked Examples
Example 1: Stock Position Sizing
Problem: Account: $25,000 | Risk: 1% | Buy AAPL at $175 with stop loss at $170.
Solution: Risk amount = $25,000 × 1% = $250\nRisk per share = $175 - $170 = $5\nShares = $250 / $5 = 50 shares\nPosition value = 50 × $175 = $8,750 (35% of account)\nMax loss if stopped = 50 × $5 = $250 (exactly 1%)
Result: Buy 50 shares | Position: $8,750 | Max loss: $250 (1%)
Example 2: Crypto Position Sizing
Problem: Account: $5,000 | Risk: 2% | Short BTC at $65,000 with stop at $67,000.
Solution: Risk amount = $5,000 × 2% = $100\nRisk per unit = $67,000 - $65,000 = $2,000\nPosition = $100 / $2,000 = 0.05 BTC\nPosition value = 0.05 × $65,000 = $3,250\nMax loss = 0.05 × $2,000 = $100 (exactly 2%)
Result: Short 0.05 BTC | Position: $3,250 | Max loss: $100 (2%)
Frequently Asked Questions
What is position sizing and why is it important?
Position sizing determines how many shares, contracts, or units to buy or sell on a trade. It's arguably the most important aspect of risk management — more important than your entry strategy. Proper position sizing ensures no single trade can significantly damage your account. Without it, even a strategy with a 70% win rate can lose money if the losing trades are too large. The key principle: your position size should be determined by your risk tolerance (usually 1-2% of account) and the distance to your stop loss, NOT by how much capital you have available or how confident you feel about the trade.
How do I calculate the right position size?
Position Size = Risk Amount / Risk Per Share. First, determine your risk amount: Account Balance × Risk Percentage (e.g., $10,000 × 1% = $100). Then calculate risk per share: |Entry Price - Stop Loss Price| (e.g., |$100 - $95| = $5 per share). Finally, divide: $100 / $5 = 20 shares. Your total position would be 20 × $100 = $2,000. This method ensures your maximum loss is exactly your risk amount ($100) regardless of the stock price. Always round DOWN to the nearest whole share to keep risk at or below your target.
How does position size change with different stop loss distances?
Position size is inversely proportional to stop loss distance. A wider stop loss means a smaller position (fewer shares), and a tighter stop loss allows a larger position. Example with $100 risk: Stop loss 2% away ($2 risk/share) → 50 shares. Stop loss 5% away ($5 risk/share) → 20 shares. Stop loss 10% away ($10 risk/share) → 10 shares. The dollar risk stays the same ($100) in all cases — only the number of shares changes. This is why scalpers with tight stops can trade larger positions than swing traders with wide stops while maintaining the same risk level.
Should I use the same position size for every trade?
No — your position size should be calculated fresh for each trade based on the specific stop loss distance. Using a fixed dollar amount (like always buying $1,000 worth) is a common mistake because it means your risk varies with each trade's stop loss placement. The correct approach is fixed RISK (e.g., always risking 1% of account), which results in different position sizes depending on the volatility of the asset and distance to your stop loss. Some advanced traders also adjust risk based on conviction level (0.5% for B-setups, 1% for A-setups), but this requires discipline and a proven track record.
How do I calculate position size for proper risk management?
Determine your risk per trade (typically 1-2% of account balance), set your stop-loss distance in pips, then divide the dollar risk by the pip value to get the correct number of lots. This ensures consistent risk regardless of the pair or stop-loss width.
What inputs do I need to use Position Size Calculator accurately?
Each field is labelled with the required unit (metric or imperial). Gather your source values before starting — for example, a weight measurement in kilograms, a distance in metres, or a dollar amount — and enter them exactly as measured. The formula section on this page lists every variable and explains what each represents.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy