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Staheli Arch Index Calculator

Tool to measure and calculate the Staheli Arch Index

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What

The Staheli arch index (SAI) is an index that provides a quantitative measurement of the plantar arch of the feet. It can be used to measure how flat your foot is.

Staheli arch index measurement

For attaining SAI a line is drawn tangent to the medial forefoot edge and at heel region. The mean point of this line is calculated. From this point, a perpendicular line is drawn crossing the footprint. The same procedure is repeated for heel tangency point. We thereby, obtain the measurement of the support width of the central region to the foot (A) and of the heel region (B) The SAI is obtained by dividing minimum sole width A value to maximum heel width B value (SAI = A/B)

How

  1. Make a footprint: paint your sole with water-based paint and stand on a piece of typewriter paper. Use a light paint similar to your skin color, because it is not easy to wash off.
  2. Scan the footprint. You can also simply take a photo, but in this case, make sure that the image is not distorted, because it will affect the SAI.
  3. Open the tool and load the picture. Open the tool
  4. You can move and enlarge the scanned image. Drag the tangent by moving the two control points, then mark the sections that fall on the foot under the perpendiculars.
  5. SAI can be seen in the upper right corner of the image.

Why

I tried several methods to cure my inflamed plantar fascia: I visited a store that sells insoles and also a physiotherapist. The seller selling the insole and the physiotherapist agreed that the inflammation could have been caused by my flat feet, but they disagreed in what the long-term solution could be. The seller claimed that in adults, flat feet cannot be corrected, only symptomatic treatment exists, insoles must be worn until the inflammation subsides. However, according to the physiotherapist’s opinion, my sole can be restored to normal with foot- and ankle strengthening exercises. It seems that the physiotherapist was right, in a few weeks my SAI decreased from 0.93 to 0.78 (the upper limit of the normal range is 0.7). This tool was created to precisely measure the SAI.