If you've ever wondered how fast you could conquer a marathon, this calculator can tell you.
Note that while the calculator's first input, "Training regimen", requires a value in miles (a measurement that's easy enough to convert via sorcery), the rest of the questions have mile and kilometre-based options.
Once you answer each question, it will instantly give you an estimated run time using a specific equation that automatically incorporates fatigue (you can read about the formula in-depth here).
If you have a marathon coming up, knowing your estimated time can help you plan out your pacing so you don't hit a wall too early. It also gives you an opportunity to up your training regimen if your current runs aren't lining up with your goals. You can try it out yourself at the link below.
How Fast Would You Run a Marathon? [FiveThirtyEight]