If you have a recent sports watch or Apple Watch, it may already include Power. Check with your watch manufacturer to see if it includes Power.
Alternatively, you can buy a Power Meter – power meters for running include the Stryd Footpod, the Garmin Running Dynamics Pod, the RunScribe Plus or Red, and the the Polar Grit or Vantage V.
Personally, I’ve used Stryd Footpods (non-wind and wind versions) since 2018 and am 100% happy with them. Plus, Stryd consistently scores highly in reviews and comparisons (fellrnr, dcrainmaker, Outside) and comes with great customer service.
For more information on Power Meters, please see the following posts:
🔹 What is a Power Meter?
🔹 Do running power meters produce meaningful numbers?
🔹 Can you use a Stryd footpod to Run with Power?
🔹 Can you use a running watch to Run with Power?
🔹 What else do you need (apart from a Power Meter)?