UPDATE CT v4.6.3
The existing tool calculates the lot size based on the balance using the leverage as part of the formula, I have found the total to be around incorrect by a small amount. The lot size is based on a % of the available margin.
£658 account with a 1:500 leverage
20% position size, will use 131 available margin as shown in the positions window.
If you are using a large account size then the maximum lot by the broker is anywhere between 10-50 lots, no matter what % you use, once it's above 10-50 lots, it will open an order at the max lot size
A new version of cTrader v4.6.3 has an API to use the formula as shown in the last post, this makes the position size and leverage used more accurate.
The new update will be published when Spotware rolls out the latest version that is in Beta, if you have purchased the product you can contact sales for the updated version, but this will only work with cTrader Beta 4.6.3
you may also request a refund here if your purchase is within 14 days.