When it comes to science of stringing rackets, it’s the numbers that tell the tale. And when it comes to numbers, we should focus on proper measurements. That’s why we decided to write a detailed post about the latest and most practical technique to check your racket string tension, whether you want to do checkups on your tennis, badminton or squash racket string tension.

As we mentioned in another post, string tension is a contributing factor to overall “stringbed stifness”, where parts of the frame, head size, string pattern and suspension system also play their part. So when we talk about checking string tension, we will actually be referring to measuring stringbed stiffness. It’s good to point out that stringbed stiffness consequently influences power, control and feel.

Stringbed stifness is measured in two ways. Dynamic stiffness refers to how much the stringbed will deflect perpendicular to the strings when it is impacted with an object of given energy, let’s say a tennis ball. So the best way to imagine this is the amount of distance the frame will bounce back from hitting a ball. The scientific calculation of course needs some explanation, but this gives you an idea of what we’re looking for.

Measuring dynamic stiffness of a stringbed is the most relevant test, but it is also complicated to measure. That’s why the most common method of measuring stringbed stiffness is via a static stiffness test. This method measures the string deflection when a force is applied slowly (so no collision impact) to a certain area of the stringbed. This normally is the centre of the stringbed. The deflection that is being measured then is the result of all stringbed factors mentioned above.

Stringbed stiffness and string stiffness (or string tension) are not the same thing, but string stiffness contributes to stringbed stiffness. String stiffness in itself is a measurement of string material and gauge.

Tourna Stringmeter

An example of a relatively cheap option to do a quick static stiffness test is to use the Tourna Stringmeter. Now it’s crucial to point out this is not the most reliable way of measuring, but it can give you a quick glance at how your string tension is doing over time. It works on a relatively simple idea of a turning mechanism that eventually lines up with your center main string to give you a reading of the corresponding string tension. If you are just looking for a cheap option, or just having a backup for your smartphone, we think it could be useful picking up a Tourna Stringmeter.

Understanding and measuring dynamic tension

There actually are some valuable tools that can help you measure dynamic stringbed stiffness by simulating an ball impact. The outcome of such tests are measured in Dynamic Tension-value (or short DT-value). Dynamic tension is ball power in kilopond (kp) required to deflect the stringbed 1cm at the sweet spot (ball impact). International standards for this are kp/cm or Newton/mm.


One of the most frequently used tools by stringers in local shops and on the tour is the ERT300 by Beers Technic Professional Sports Equipment. It’s a tool of great quality and priced as such at 192 euro.

  1. Clip the ERT300 to the strings
  2. Push the start button to automatic measurement
  3. Wait a few seconds and read the values.
  4. Use the included DT system disc to determine string tension in kp (lbs)

Included in the kit are the ERT300, a soft case of 20x20x4cm, manuals in English, Deutsch, Francais and Italiano, the DT-system disc (to calculate the appropriate string tension), 2 CR2032 batteries. However, as mentioned by one of our readers in the comment section, the ERT300 unfortunately seems to be out of stock all over the web. Luckily, there is a great alternative now and that is the MSV Ministt, which you can order here at Racquet Depot UK and ships worldwide. As a bonus, it’s priced quite a bit cheaper then the ERT300 at 72 euro.


RacquetTune is one of the first mobile applications that was developed to create a more practical way to measure your string tension (more frequently). All you need to do is tap the strings – RacquetTune then uses the sound generated to calculate the tension. In addition, the interactive swingweight calculator aids in customizing your racquet to fit your own stroke pattern, while the stiffness calculator allows you to simulate different combinations of strings and tension. We will actually test this feature in another post.

Tension measurement

  • A quick and easy way to determine tension and stringbed stiffness.
  • Able to detect changes in tension as small as 0.1 kg/0.2 lb.
  • An accuracy indicator ensures consistent results.
  • Graphical presentation of sound waves to help you find the ideal way of tapping the strings, in order to obtain the highest possible accuracy.
  • Racquet and string data can be saved for further analysis.
  • Settings can be customized for tennis, squash, racquetball and badminton racquets, respectively.
  • View the tension history for each racquet as a list or a graph.
  • Email a spreadsheet with test data

Swingweight calculator

  • Add as many weights as you wish to the frame.
  • Move and change weights to visualize how swingweight, balance and sweet spot location are affected.
  • Enter target values for the racquet and let RacquetTune distribute the weights automatically.

Stringbed stiffness calculator

  • Simulate various racquet and string configurations.
  • Vary tension, string type, and racquet head size.
  • Shows load-displacement curves, stiffness and elastic energies.
  • Handles the large deformations encountered in actual play.


TennisTension claims to be the first working mobile app that instantly measures the momentous string tension of a tennis racquet with extreme consistency and accuracy (the error is less than 0.2 kg). However, we doubt this is actually the case because RacquetTune was the first app to our knowledge. TennisTension tracks the tension loss of the racquet’s string all the time from the moment the racquet is strung. It records and analyzes the ringing sound heard from the strings when they are hit anywhere with any stiff object (pen, pencil, another racquet, fingernails, et cetera). Hybrid strings also can be measured. The app calculates the average tension between mains and crosses. If a racquet is strung 24/23kg, then the shown result will be 23.5kg.

It has a feature to put a specific profile for everything stringer that you use. Every different stringer puts different tension compared with another when they are told to put the same tension. Define the type of “Stringing”. For example, if the stringing machine is in a very good condition and/or the stringer is a very experienced one, then the user must choose “tight” or even “very tight” from the popup menu of the “stringing” button.

The team behind TennisTension claims that the app has been systematically tested with different racquets and strings by players at a different level of play – from beginners to ATP professionals. However, when we tried to lookup more information on the app, we couldn’t reach the website.


The team behind Stringster claim to have developed their app exclusively for badminton players, but at first sight their technology and features seem to match up pretty comparable to RaquetTune and TennisTension. The reason as wo why to market this specifically as an badminton app, is something we would really like to know because at first sight, the app really is looking good.

Update: and luckily, our prayers have been heared! The team behind Stringster now has released a tennis edition of their app and I am super excited to test if it seems to work just as good. I’ll be updating this article as soon as possible.


In the long term, by using an app to measure your string tension regularly, every player can improve his on court performance by choosing the right string and racquet model, the relevant string tension, adjusting it better with the playing conditions, understanding, tracking and coping with the tension loss, and adjusting faster to the way the different stringers string at various sites and tournaments. Apps of course are practical, because almost everybody has a smartphone which makes checking regularly very easy. However, when it comes to accuracy, the DT check of the ERT300 still gives the most reliable results, time after time. If you are a stringing hobbyist, we definitely understand your decision to go for an app, but if you are a professional stringer you might definitely want to free up some budget to invest in an ERT300 or MSV Ministt.

Leave a Reply

  1. Love Tennis Blog

    Great article.
    It’s a shame the Ert300 is no longer available anymore. Tennis players and stringers really need a reliable replacement.

  2. David

    It’s worth mentioning that whilst RacquetTune is available to buy on both iOS and Android, only the iOS version is currently supported. The Android version is missing a lot of features, and the embedded help links return 404 Not Found errors. (this is from someone who bought on Android following reading this review and was sadly disappointed to find only a part-functional app)

    1. Bob

      Hi David, thank you very much for your comment and your information. Of course, nobody wants a partly functioning app so this is something we’ll definitely add to the article. By the way, have you tried to get a refund from the Google Play Store? Best regards, Bob.

      1. David

        No problem Bob. FYI I looked into it a bit further – the app developer only supports the iOS version of RacquetTune. The Android version was ported over by a 3rd party at an earlier version but it was a “one-and-done” affair so it gets no updates.

        The biggest difference I’ve spotted is with String Factors (SF) that are used in the calculation of tension. The iOS version has a live database of SF values built up from app users, so when you put in a string you can look to see what values other testers have used (it can be measured, but only if you have the right equipment).

        The Android version, on the other hand, does not have this database at all. You have to either use a default SF or put one in yourself manually. This can lead to a fairly significant discrepancy in the measured tension.

        (for reference, using the default Polyester SF for a string I installed at 51lbs gave a reading of 56lbs from the app. When I remeasured using a specific SF that I got from a stringer I spoke with, this gave reading of 51.4lbs from the app)