Best Position Size Calculators in the UK

OK, so you’ve decided risk management is important, now, how do you choose a position size calculator to help you manage stocks and forex risk? Which one is best? Well here’s a definitive guide to the best calculators available online.

Let’s get into it.

Quick Background

When it comes to trading, knowing your position size isn’t optional—it’s fundamental. Whether you’re trading stocks, forex, or indices, the right position size protects your capital and keeps your risk per trade in check.

There are lots of tools online that can help, but not all are made equal. Some are built for forex only. Others give you raw numbers without much context. A few look like they haven’t been updated since 2011.

Top 5 Position Size Calculators

1. PositionSizeCalculator.co.uk (Best Overall)

Position Size Calculator is the calculator we created because I needed one that actually made sense for both stock and forex traders. Most of what was out there was clunky, overly technical, or didn’t give me enough flexibility or allow me to calculate stocks at all!

Why it stands out:

• Handles Stocks, Forex, and Indices in one place.
• Works with GBP, USD, and EUR accounts.
• Lets you enter either stop loss in price or percentage.
• Clearly shows leverage impact, risk per trade, and number of shares/lots.
• Converts % of account to invest into money value.
• Includes extra options like timeframe, broker selection, and experience filter.

In seconds, you get a detailed trade summary that includes:

• Number of shares or lots
• Amount at risk
• Per-share cost
• Overall risk rating
• Risk:Reward ratio

And it looks good too—clean UI, responsive, and made for actual traders.

Example Output:

You selected a BUY position for AAPL with 5:1 leverage on the 5m timeframe. Your calculated position size is 13 shares at £150.00 per share, with a stop loss of £140.00 (6.7%) and take profit of £200.00 (33.3%). You’re risking £26.00 of your capital with a Risk:Reward ratio of 1:5.

(See screenshots above)

2. Lot Size Calculator

2. Lot Size Calculator (Best for Forex)

Lot Size Calculator is a sleek, modern tool built for forex traders. It’s one of the few calculators that balances user-friendliness with depth—and while it doesn’t support stock trading, it offers one of the clearest forex calculators available.

Why it’s solid:

• Designed specifically for forex traders.
• Supports GBP, USD, and EUR account currencies.
• Offers standard and lot-based modes.
• Inputs include account balance, risk %, stop loss (in pips), take profit (in pips).
• Traders can select buy/sell direction, timeframe, broker, and experience level.
• Results include:
  • Calculated lot size
  • Amount at risk
  • Pip value
  • Risk rating (Low, Medium, High)
  • Risk:Reward ratio
• Features a visualised risk assessment quadrant.
• Allows users to copy settings or save results.

Example Output:

You selected the 15m timeframe for a BUY trade. Your calculated lot size is 2.00, with a stop loss of 20 pips. That means you’re risking about £400.00 on this trade. Your risk is rated High because your amount at risk is Medium but the asset has low volatility. Your potential Risk:Reward is 1:5.

Only downside: It doesn’t support stock position sizing—so if you’re trading equities, you’ll need something broader like PositionSizeCalculator.co.uk.

But for forex traders, this is an incredibly powerful and easy-to-use tool.

3. MyFXBook Position Size Calculator

MyFXBook has been around forever in the forex world. Their calculator is solid if you’re purely a forex trader, and want something fast and reliable.

Pros:

• Simple to use.
• Great for calculating position size in lots.
• Trusted and widely used.

Cons:

• Forex-only (no stocks, indices, or share trading).
• Lacks visual summaries or trade context.
• Doesn’t help newer traders with interpreting the data.

It works well, but feels a bit dated and narrow in scope.

4. BabyPips Position Size Calculator

Another classic for forex traders. BabyPips is fantastic for learning the basics, and their tools are clean and straightforward.

Pros:

• Educational, with tooltips and guides.
• Clean UI for forex traders.

Cons:

• No support for stocks or share-based position sizing.
• A bit too basic if you want layered inputs like account currency, leverage, or experience.

Still a useful calculator—but best if you’re brand new and just trading major forex pairs.

5. Earn Forex Position Size Calculator

Earn Forex’s position size calculator is designed with prop traders in mind, particularly those taking part in their Gauntlet and Bootcamp challenges.

Pros:

• Focused on futures and forex.
• Integrates with their funded account programs.
• Gives quick calculations in contracts.

Cons:

• Doesn’t support stocks.
• A bit more niche, mainly useful if you’re already part of Earn2Trade.

Still, it does its job well for those trading in the futures and FX space.

Final Verdict

For stocks and forex calculations, Position Size Calculator (positionsizecalculator.co.uk) is the best If you’re only trading forex then Lot Size Calculator (lotsizecalculator.co.uk) or even MyFXBook (myfxbook.com) might do a good job.

Both Position Size Calculator and Lot Size Calculator were built with real traders in mind. It shows you what matters in a clean, well-designed UI that’s easy to understand and was built in 2025, not 2011.