For normal, flat tracks in Minecraft, the commonly recommended setup is:

  • Put 1 powered rail about every 38 blocks of track to maintain top speed on a minecart with a player in it.
  • That works out to roughly 37 regular rails in between each powered rail on level ground.

A simple way to think of it:

  1. Place a powered rail.
  2. Then place up to 37 normal rails after it.
  3. Repeat with another powered rail.

This spacing keeps your cart moving quickly without wasting gold on too many powered rails, though using them a bit more frequently (every 20–30 blocks) will feel snappier, especially for uphill or loaded carts.