"How high is the kite" is an everlasting question.  It is common to speak of the height of a kite, however the exact term is elevation.
Here I summarizes the main elements of investigations and developments I started in 1992 to determine the elevation of a kite.
The elevation of kite can be a concern for some scientific experiments, where there are some regulations on the height of kite, or because of applications such as kite aerial photography.
Setting an altimeter on the kite is an accurate way to measure the elevation of the kite. Electronic devices are becoming cheaper. The only difficulty is to send the data to the ground. There are some solutions.
One similar way can be to have a GPS device.
Telemeter is a wonderful device. If you can walk under the kite, and target it, here is the height!
Otherwise, measure the distance D to the kite and the angle b between kite and horizon, then apply the formula
  H = D x sin b
The accuracy of this method depends mainly on the measurement of the angle, and ends to ±4%.
Unfortunately, telemeters for distances greater than 20m are very expensive. Too bad.
A re-designed protractor is useful for angle measurement. Difficult to be better than ±2°.
Without any electronic device, we can estimate the line length. Some kiters, and many kapers are marking their lines, every 100m and/or every 50m.
With this method, the line is considered as straight, when in fact, it is curved. So the calculated height is normally always greater than the true one. In fact, there is also the elongation of the line under stress:
Kevlar -> 2%
dyneema -> 3%
Polyester -> 10%
Polyamide -> 20%
  under the maximum stresses.
There are different shapes of curves of the kite lines. They depends on the kite pull, the length and size of the line, its weight, the pull of the wind on the line.
The mathematical equation of such curve shall take in account these physical parameters, and it makes it quite complex.
The figure shows how different the curves of the line can be.
I have tried to find more simple way to get an acceptable result. For all of them, the length of line have to be known, and angles have to be measured.
I have first considered calculations based on angles of kite direction, and of kite line.
Here below are the different methods I have established.
In the Cerf-Volant Club de France magazine, Le Lucane N° 72, June 1995, I published a paper with a formula. I considered the true height NK half way between the triangle calculation TWM, and between another VC supposing the line is following two straight lines. These straight lines are one oblique TJ, as line angle at anchor point, the second JC is vertical. They are such as their total length is equal to the line length L.
During the next years, I remarked that this method is always underestimating the height as calculated. However, it is often largely compensated by the material elongation.
This method is also more appropriate and result more acceptable when there is a load hanging at J, such as a kap rig.
Anyway, not satisfied enough, I successively draw two other ways to follow the line curve.





This one is similar to the Lucane 72 method, but the vertical segment JC is now inclined, following the line angle at the bridle of the kite. The length of TJ + JC is equal to the line length TSK.

In theory, the calculated height VC is always a bit lower than the true one NK. On the figure, the difference is shown exaggerated for clarity. The difference is guessed something like 1 to 1,5%. There is much more uncertainty from angles measures and line length estimation.

To know the line angle at the bridle, it needs to walk leeward to be able to align with JK. Or the line angle g can be measured after take off with 30m line release. It is then necessary to know this angle in different wind conditions, but experience has shown that it is then quite predictable.


The tangent segment method looks good in theory, but being obliged to know or measure the line angle at the bridle of the kite is not so practical and it adds some uncertainty to the result that this other method doesn't have.
The arc of circle is tangent at T with the line. The arc TJC is equal to the length of line TSK. I is the middle of TC.
 For clarity on the figure, C is shown below the kite. In fact, it is close to K, and it may be over K in some cases.
Like the Lucane 72 method, this one needs the two angles a and b and the length of line. Surprisingly, the calculation results are very close to those of the tangent segments method, and usually just over.


From the formulas, it is easy to draw tables. A good way is to calculate for a line length of 100 (whatever m or feet) and fill the table. Then multiply the calculated result by the actual length and divide by 100 to have the actual height.

There is an Excel file that can be downloaded. It has calculation sheet for each method, a sheet for comparison of the method, and a useful simulation sheet which can be filled with the most common datas of several kites, giving fast results to the usual cases occurring with our personal kites.

The comparison and the simulation sheets also calculate the base TV which is useful when kaping for positioning the kite at the proper place.

Download takoteur·becot.xls


These are for a Rokkaku and a Flowform. The length of line is 100.
It clearly shows that there is not a big difference of results between the four methods: no more than 3% on these above theoretical calculations. Uncertainty on angle measurements is 4% or greater. Uncertainty on line length can be much more: 180m instead of 165m is 9%.
Don't forget also that stretching of the line can be great, depending on material of the line.