What size should the position be?

Fix the money you are risking, then let the position size fall out of the arithmetic. Never the other way round.

Where the numbers come from

On most major pairs quoted to four decimals, one pip on a standard lot is worth about $10. Your platform shows the exact figure for the instrument you are trading — use that if it differs.

The consequence beginners get backwards

A wider stop means a smaller position, not a bigger loss. The money at risk stays fixed at your 1%; only the size changes. Beginners keep the size fixed and move the stop instead, which is how a 1% plan quietly becomes a 15% loss.