The Persian foot was slightly larger than the well-known English foot.

According to The Lost Science of Measuring the Earth by Robin Heath and John Michell, it was based on the foot of Darius at exactly 1.05 British feet, which converts to 32.004 cm, while Howard Crowhurst, in his video (and presumably book) pegs it at 32 cm. Wikipedia of course is happy to claim a mere 300 mm (citation required…).

We can relate this to the cubit with reasonable accuracy. Remember that the normal British foot is 1/5th of Grand Metre (1 metre plus 1 royal cubit).

The Persian foot, on the other hand, is simply the Grand Metre divided by (pi + phi).

Here’s the pictures:

Persian foot

The difference (using 1 + π/6) comes out at 0.000068884 m. Pretty close. Not something you would notice on a ruler.