When I published my detailed write-up on the science of critical speed for runners, I promised that I would code up a free calculator to calculate your critical speed (also known as “critical velocity” or CV) from a set of race performances. That calculator is now finished!
⏱️ Try my critical speed calculator here! ⏱️
This free web app makes it super easy to implement the statistical calculations that give you critical speed—and its uncertainty bounds—given a set of race performances.
Like all of my web apps, it’s designed to be mobile-friendly, and it includes cookie-based “memory” so you can come back to where you left off. This critical speed calculator is also super easy to use: you don’t have to convert race performances into seconds, and you can choose from a wide range of pre-set race distance options, or enter a custom distance.
This is the only critical speed calculator I know of that gives you statistically appropriate uncertainty estimates that you can use for physiologically based workouts.
CS-minus (CS-), for example, is the speed at which you have a 90% chance of being in a metabolic steady-state. That property makes it a very useful upper limit for threshold workouts, where your goal is to come close to—but not exceed—your maximal metabolic steady state (SSmax).
The same is true for VO2max workouts: CS-plus (CS+) is the speed at which you have a 90% chance of being in a metabolically unsustainable state—which is the goal when you’re doing “VO2” workouts.
Critical speed, critical pace, critical power, and critical velocity
It’s worth a quick refresher on the relationship between the various “critical” terms you may hear thrown around. For runners, the modern, physiologically appropriate term is critical speed or CS. That’s what you’ll see in all of the latest scientific papers. In cycling, the analogue is critical power or CP—the reason being that, in cycling, you can measure mechanical power output (via the crankshaft). No such calculation is possible, or appropriate, in running.
In running, the critical speed model implicitly assumes that your running economy is constant across different speeds, so (in this model) speed is power output—though with the caveat that it’s metabolic power, not mechanical power. So, when a device like a Stryd pod or a Garmin or COROS watch is telling you about your “power output” or your “critical power,” that’s referring to your metabolic power output, not any kind of mechanical measurement like in cycling.
An older term for critical speed is critical velocity or CV. Some older scientific papers used that term until biomechanists chided them about the fact that “velocity” implies speed and direction. Before the change-over in terminology, though, “critical velocity” and “CV pace” became popularized in the running world, in part due to the success of Drew Hunter and his coach, Tom “Tinman” Schwartz.
Occasionally you will see critical speed referred to as “critical pace,” since most runners train by pace (minutes per mile, minutes per kilometer), not literal speed (meters per second). But the underlying math is exactly the same, and I prefer to stick to the scientifically appropriate term even though this app is also a critical pace calculator.
Getting critical speed from just one race performance
One downside of the critical speed model is that you need a minimum of two performances to get an estimate for critical speed, and three performances to get an uncertainty range.
One workaround I’ve developed is implemented in my threshold, CV, and VO2max calculator, which pools data from many runners who have completed several different race performances, then uses a statistical model to estimate the range of values for CS / CS+ / CS- that are plausible for you, given just one race performance. Obviously the “full” critical speed is more scientifically accurate, but often you’ve got to work with what you’ve got.
⏱️ Calculate your critical speed here ⏱️
Learn more about the science of running
If you want to apply a more scientific approach to your own training, I have two books that outline exactly how to do it. The most recent is Marathon Excellence for Everyone, which takes a full-spectrum percentage-based approach to running your best in the marathon.
If you live outside of the United States, Marathon Excellence is also available in a Metric Edition, with all workouts in kilometers!
I also have a shorter book, Modern Training and Physiology for Middle and Long-Distance Runners, that covers a simpler scientific approach to 800m–10k training. Check it out!
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