Perhaps an example
Say I think DASH is likely to go up from a current price of 0.02519, but if I'm wrong I want to bail at 0.0249, with a view to selling the trade at 0.0259 if I'm right.
So my stop loss is to be set at 0.0249 and lets say I'm comfortable risking $100. What quantity would I buy at 0.02519 and stop at 0.0249 for that risk to equal $100?
Okay, so first step normalize what currency you're spending/thinking about. So let's make 0.02519 = 151.14 (I used $6000 for bitcoin price for simplicity) and the same for 0.0259 = 155.4 and 0.0249 = 149.4.
So: Price = 151.14, stop loss equals 149.4 and target sell price =155.4
Subtract the price from the stop loss price - 151.14 - 149.4= 1.74
Then divide that by the original price to get the percentage loss in decimal form (if your stop loss is hit) 1.74/151.14 = 0.0115 (rounded to 3 decimal places) or about 1.15%
Now the last stop is dividing your desired risked amount $100 by 0.0115- 100/0.0115=8695
So you could invest $8695 dollars, or 1.45 btc (if price was $6k)
If you also work out the upside, that is when the price hits the sell price of 155.4 dollars, you'd make $4.24 which is a 2.8% profit (0.028 in decimals).
Dividing 0.015/0.028 you get 0.53. Which means that the price would have to hit the sell price 53% of the time for you to make a profit in the long run.
I hope all that helps.