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Sunday, January 20, 2013

Pedometer Buying Guide

Pedometer Buying Guide

I have wanted to try a pedometer for years, but have not been able to pry the money out of my wallet.  There are several promising models in the under $30 price range:

Small pedometer and ear buds for radio
Mio Step 2 Pedometer
Image source: Dr. Penny Pincher

  • MIO Step 2 Pedometer, $17.  Uses "classic" 1 axis pendulum sensor, must be mounted vertically to count steps accurately.  Includes FM radio with ear buds.  Also has stopwatch, clock, and alarm clock.
  • MIO Trace ACC-TEK Pedometer, $16.  Three axis sensor, Three axis sensor, claims accurate step count at any angle.  7 day memory.
  • Omron HJ-321 Tri-Axis Pedometer, $17.  Three axis sensor, claims accurate step count at any angle.  7 day memory.
  • Omron HJ-112 Pocket Pedometer, $23.  Dual axis sensor, can be positioned horizontally or vertically.  7 day memory.  Modes for two walking speeds-regular and brisk.
  • Ozeri 4x3razor Digital Pocket 3D Pedometer, $29.  Three axis sensor, claims accurate step count at any angle.  7 day memory.

I found the MIO Step 2 at a store closing sale marked down from $16.99 to $7.48 and decided to give it a try.

Pedometer Test Drive

How accurate is a pedometer at measuring walking distance?  The sensor in a pedometer is able to count the number of steps that you take.  The pedometer converts this to walking distance using your stride length.  How does it know your stride length?  You input this based on what you think is your average stride length.  The fact that your stride length varies somewhat is the fundamental limitation on the potential accuracy of a pedometer to measure walking distance.

I clipped the Mio Step 2 on my waist after about 10 minutes of reading the direction sheet to figure out how to use it.  One of the steps is to determine your average stride length.  I laid out a tape measure in my garage and took 6 "normal" steps.  I divided the total distance by 6 to get my stride length.  The Mio Step 2 has a stride input mode where you can enter your stride length in inches.  My entry was: 26 inches.

I went on a walking trip and recorded my step count and calculated miles walked.  At home, I used Google Map Pedometer to check my route on a map and figure out the distance.  The results were not impressive.

Pedometer Distance Accuracy Using 26 Inch Stride
Image source: Dr. Penny Pincher

The distance from Google Map Pedometer is not perfect, but I would expect accuracy on the order of 10's of feet.  The Mio Step 2 had significant error, about 15% or about 600 feet of error on a short walk!  Then I realized that this measurement is very sensitive to stride length.  I took the route distance in miles, converted to inches, and divided by the number of steps to get 30.8 inches.  I decided to try the same walk again using an input value of 31 inch stride length.  I repeated the same route twice to check step count consistency.

Pedometer Distance Accuracy Using Calibrated Stride (31 inch)
Image source: Dr. Penny Pincher

Much better.  I would say as a rule of thumb you could expect the accuracy limit of a step-counting pedometer to be about 3% distance measurement error due to variation in stride length.  On both of the runs in the table above, I followed the same route at the same pace with the pedometer mounted vertically on my waist.  I have pretty good confidence in the step count, so the difference must be due to variation in my stride length.

Is a Pedometer Worth the Money?

If you want to keep track of your calories burned or distance walked, a pedometer could be a useful tool.

However, you can get a pretty good indication of how far you walk and how many calories you burn just by keeping track of the time.  For example, if you walk 4 mph and you go for a 1 hour walk, your distance is 4 miles.  If you burn about 300 calories per hour walking, and walk for 1 hour, then you burned 300 calories.

Also, if you walk the same route frequently, a pedometer will not be useful.  The main benefit of using a pedometer is to help keep track of walking in new places or if you take a variety of different routes.  Also a pedometer could give you a sense of your overall calorie consumption from walking throughout the day.

You can't go too far wrong in this price range.  If it helps motivate you to exercise and reach ideal weight, I say it's worth the money.

Mio Step 2 Pedometer Review

The Mio Step 2 has an FM radio, which is a nice feature.  It uses a CR2032 coin battery to run the radio.  With 225 mAh of power, I would expect it to run the radio for about 16 hours.  The computer/display uses a LR1130 button battery.  One concern was how much it will cost to replace the batteries- if the batteries cost more than $10 to replace, I'll probably never do it.  Good news- according to research at, replacing both batteries will cost about $1.50.

Other features include a clock, stopwatch, and alarm clock.  The pedometer calculates calories burned on your walk using your body weight, distance walked, and time.

I did a 3 foot drop test of the Mio Step 2 onto a hard surface.  Accidently.  The Step 2 survived without damage.  The drop test was performed before the test drive.

I like the small size of the Step 2.  The only problem I have is that it is a bit awkward to keep it clipped to my waistband to keep it in the required vertical position.

Pedometer Recommendations

So which one to pick?  All of these pedometers have the fundamental limitation of measuring number of steps to determine distance walked.  Since your stride length varies, the accuracy is somewhat limited.  The models with 3 axis sensors would be much more convenient for most people.  The Mio Step 2 must be mounted vertically to count steps- clipping it to your waist is the only good place to mount it.

I recommend a 3 axis model that can be carried in a pocket, backpack, bag, purse, etc.  A 3 axis pedometer is much more convenient, and you are more likely to use it.

Here are some deals on 3 axis pedometers from

  • All step counting pedometers are limited in accuracy since your stride length will vary.  Rule of thumb: expect 3% distance error.
  • Calibrate your stride length on a walking trip of a known distance
  • Look for a 3 axis sensor- this allows pedometer to work while carried in a pocket, etc.
  • A light on the display would be useful for night walking
  • A stride calibration feature would be useful- press buttons to indicate start and stop of a walk of a known distance, for example from one mile marker to the next on a walking trail.  The pedometer would automatically calculate your stride length.

Star Rating for Pedometers in General
Image source: Dr. Penny Pincher

Star Rating for Mio Step 2 Pedometer
Image source: Dr. Penny Pincher
Recommended Reading:
Walking: How fast can you walk? How long does it take to walk a block?
How Long Does It Take To Walk X Miles or X kilometers?

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