# Convert RPM to Watts/MPH on a stationary cycle? **URL:** \ **Category:** Factual Questions\ **Created:** [January 15, 2005, 3:58am UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816 "2005-01-15T03:58:50Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Yamirskoonir](https://avatars.discourse-cdn.com/v4/letter/y/c0e974/32.png) [@Yamirskoonir](https://boards.straightdope.com/u/Yamirskoonir)\ **Post date:** [January 15, 2005, 3:58am UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816/1 "2005-01-15T03:58:50Z")
Well folks, I’m doing it. I’m journaling (and limiting) my caloric intake, and hitting the gym 5-6 days a week. Recently, I’ve had stabbing pain in my right foot from an old injury, so I’ve been going for low-impact on the stationary cycle. However, the machine in my gym only shows RPM and not Watts/MPH, so I have no idea how fast I’m going and therfore can’t correctly estimate the calories I’m burning. I also can’t seem to find a converter on the internet, even after googling, nor can I find a chart that tracks calories burned by RPM. I realize that varaibles like gear ratio and wheel size and incline/resistance would normally factor in, but I’m hoping that most staionary machines are similar across the board…anyone happen to know the conversion, or know of a chart that calculates calories burned given bodyweight and RPM? For anyone wondering, the calorie guide I’ve been using is the one provided by [Calorie King.](http://www.calorieking.com/tools/exercise_calories.php) Thanks in advance! ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [January 15, 2005, 4:24am UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816/2 "2005-01-15T04:24:23Z")
measure the radius of the wheel in inches (radius of wheel) (1 mile/63360 inches) (1 Hour/60 min)= mph. ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [January 15, 2005, 4:25am UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816/3 "2005-01-15T04:25:47Z")
that isn’t right: (radius of wheel) (1 mile/63360 inches) (60 min/1 hour) (2\*pi)= mph. ---
**Author:** ![Yamirskoonir](https://avatars.discourse-cdn.com/v4/letter/y/c0e974/32.png) [@Yamirskoonir](https://boards.straightdope.com/u/Yamirskoonir)\ **Post date:** [January 15, 2005, 5:19am UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816/4 "2005-01-15T05:19:34Z")
> [@treis](#): > > that isn’t right: > > (radius of wheel) (1 mile/63360 inches) (60 min/1 hour) (2\*pi)= mph. Thanks **treis** , that will definitely come in handy when I can finally afford to buy a real bike and make use of all the wonderful hills and bike lanes where I live. Unfortunately, it’s a stationary cycle and there is no wheel, just a resistance band hidden within the machine. I was hoping there was some sort of standard of “invisible wheel” across different models of machines, but that’s probably not the case. ☹ Maybe if I contact the manufacturer, they can give me the specs? Thanks again for that formula! ---
**Author:** ![wolf\_meister](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolf_meister/32/15202_2.png) [@wolf\_meister](https://boards.straightdope.com/u/wolf_meister)\ **Post date:** [January 15, 2005, 5:33am UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816/5 "2005-01-15T05:33:07Z")
**Yamirskoonir** If you need to look for conveters, I’d say the ones on my site: [http://www.1728.com/indexcon.htm](http://www.1728.com/indexcon.htm) have probably got what you need, - that is _after_ you have determined how much energy is required to power that stationary bike. Let’s face it, the tension on that resistance band would determine just how much energy (or calories) is required. As you probably know, going 1 mile with zero resistance won’t burn as many calories as going the same distance with a great deal of resistance. Your idea of contatcting the manufacturer would be your best choice. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [January 15, 2005, 5:41am UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816/6 "2005-01-15T05:41:25Z")
I think there’s so much variation that one can’t provide a “typical” conversion factor. Perhaps you could invest in a heartrate monitor? Most models will give you an estimate of calories burned. ---
**Author:** ![threemae](https://avatars.discourse-cdn.com/v4/letter/t/5f9b8f/32.png) [@threemae](https://boards.straightdope.com/u/threemae)\ **Post date:** [January 15, 2005, 3:33pm UTC](https://boards.straightdope.com/t/convert-rpm-to-watts-mph-on-a-stationary-cycle/284816/7 "2005-01-15T15:33:28Z")
Agreed. If you want to really accurately measure your power, you are going to need either an SRM or Powertap ([www.cycleops.com](http://www.cycleops.com)) and both are looking at $900-1500. If you are only doing this for weight-loss/fitness reasons, then use an HRM in conjunction with a chart for body size, activity, intensity, and approximate calories burned, or an HRM that will do this automatically.