How accurate are smart scales?

Are smart scales accurate weighing instruments or just simple bathroom scales with expensive connectivity features? To find out, I tested the Withings WS-30, Fitbit Aria and A&D UC-324NFC using class M1 weights.

Preparation

Each of the scales had not been used before and was configured as instructed by the manufacturer. This included signing up for an account with Withings and Fitbit. In the case of A&D’s UC-324NFC, I took advantage of a function available in the Wellness Connected  app which let me “calibrate” the scale by entering the local gravitational acceleration.

The scales were tested under similar conditions with a stable temperature of around 22°C and were placed on a flat, hard surface. The Withings and Fitbit scales were left alone for a night after the initial configuration as I wasn’t quite sure how they determine the zero value: unlike older electronic scales, you don’t have to switch them on and wait for them to show ‘zero’, instead, you step right on (the UC-324NFC determines the zero point after you step off).

Test procedure

I used 20kg weights to test the scales at 40, 60, 80, 100 and 120 kg. This procedure was repeated 3 times for each scale (I did a lot of weight lifting that day).

Results

The first column gives you the nominal weight (in kg) and the next three are the values as shown by the scales.

Withings WS-30

40 40.2 40.2 40.2
60 60.3 60.3 60.3
80 80.4 80.3 80.3
100 100.3 100.4 100.4
120 120.4 120.4 120.4

Fitbit Aria

40 40.2 40.2 40.1
60 60.2 60.2 60.2
80 80.2 80.2 80.2
100 100.3 100.3 100.3
120 120.3 120.3 120.4

A&D UC-324NFC

40 39.95 39.95 39.95
60 60.00 59.95 60.00
80 80.00 80.00 79.95
100 100.00 100.00 100.00
120 120.00 120.00 120.00

As you can see, A&D’s UC-324NFC was the most accurate scale, never deviating by more than 50g from the true value. Its 50g resolution and gravity compensation function certainly paid off.

However, the Fibit and Withings scales did a great job, too. Looking at the measurement results in each row, you’ll see that they are either identical or off by just one scale interval (100g). We can therefore say that these scales were slightly less accurate, but still very precise* (or that their repeatability was still excellent). As far as your body weight is concerned, you’ll generally be less interested in absolute values and more in tracking changes (“am I loosing or gaining weight”) and these scales would be perfectly suitable for this purpose. Nevertheless, I was a bit surprised that Fitbit and Withings didn’t use the location I had entered during account creation to adjust the scale for the local gravity acceleration. This would most likely have improved their accuracy.

Overall, the results are very good. As far as I can tell from this test, you’re not just paying for the “smart” features, you get accurate scales, too.

Further information / where to buy:

Disclosure:

  • Some links above are affiliate links.
  • My company used to sell A&D’s UC-324NFC in our German scales shop, but we don’t anymore. The Withings WS-30 and Fitbit Aria were purchased at retail prices, A&D’s UC-324NFC was purchased with a dealer discount.

*Meaning of accuracy and precision (as used in this article):
Accuracy and precision explained

Near Field Communication: A&D’s new wireless UC-324NFC scale

The following short video shows A&D’s new wireless UC-324NFC scale in action. It is the first scale in the world with an integrated NFC chip, making it very easy to transfer your weight to your smartphone. Currently, this only works on Android with A&D’s own WellnessConnected app:

Personal scales: a look back at Medica 2012

With over 4,500 exhibitors, MEDICA in Düsseldorf (Germany) is the world’s leading medical trade fair. I managed to visit the following stands last year to have a look at the newest personal scales (aka bathroom scales, bedside scales, medical scales):

A&D Medical

A&D exhibited their new line of NFC-enabled products:

  • UC-324NFC personal scale
  • UA-767NFC blood pressure monitor
  • UW-101NFC activity monitor

You can see them in action in the following video, which was also showing at the booth:

I used my HTC One X smartphone to download A&D’s Wellness Connected app, weighed myself and then transferred the weight by just holding the phone close to the scale. It doesn’t get any easier. With NFC, there’s no need to configure a WLAN or Bluetooth connection for your smart scale, just tap and go. Other than storing the weight on your smartphone, the app also gives you the option to upload it to Microsoft’s HealtVault, turning it into a veritable internet scale (without additional costs or subscription fees).

A&D medical’s new NFC products are already available in the UK from A&D’s wellness connected Webshop and from other shops such as:

The devices are being introduced to the German market this week at the CEBIT trade fair. German customers will be able to buy them from our German scales shop in just a few days. Update March 6: A&D’s UC-324NFC precision personal scale as well as the UA-767NFC blood pressure monitor and UW-101 activity monitor are now available in our German scales shop.

A&D’s MEDICA 2012 report can be downloaded here (PDF).

Seca

Wireless communication was one of the main topics at Seca, too. Weight and height can easily be transferred to an indicator, printer or computer with seca 360° wireless technology. Other topics were the Seca mBCA (medical Body Composition Analyzer) and Seca’s analytics 115 software.

Kern

While Kern’s complete catalogue is approaching phonebook dimensions, the stand at Medica stood out by it’s clear simplicity and focus on just a few products. The most interesting ones are the the new MPC, MPD and MPE series of verified medical scales (which are replacing the MPP series):
Kern MPD 250K100M medical scale

With list prices currently starting at 246,- EUR (+46,- EUR verification costs + shipping) for the MPD (shown above), GPs who still use unverified cheap bathroom scales have no more excuses!

The scales might not look as nice as Soehnle Professional’s “Vemano” design series and they don’t have any wireless communication capabilities, but then again, they start at 246,- EUR. Fierce competition between Kern dealers could lead to even lower market prices.

Other products shown were a new baby scale and wheelchair scale.

Adam Equipment

Unlike other companies, Adam Equipment traditionally shows a larger variety of scales at Medica, including precision scales for lab use. Some scales like the PGW and PGL series really have to be seen up close and personal to be fully appreciated. A picture without size references doesn’t do justice to the enormous display, so here’s me holding my not-too-tiny hand close to it:

My hand close to the giant display of Adam's PGW precision scale

This picture was actually taken at ACHEMA. I promise to take more and better pictures at future trade fairs.

Among the medical scales, the new MUW 300L with integrated ultrasonic height measurement and BMI calculation stood out by it’s shear size. I was, however, assured that it can easily be disassembled for shipping. Here’s a photo of one of Adam Equipment’s friendly employees standing on the MUW 300L with me standing on the floor:

MUW 300L at Adam Equipments stand at Medica 2012

Suitable for people up to 210cm tall.

Other scales manufacturers at Medica:

(unfortunately, I only had time for a quick glance at their stands)