Ultrassonic thickness gauge

Hi everyone, I would like to build an ultrassonic thickness gauge using an arduino and one or more chinese ultrassonic sensors (costs a few bucks each). The obvious question is precision. It would be used on sheets of rubber, foam and eva. I need a precision of at least 0.1 mm. My idea would be to position the sensor at a certain fixed height facing a flat surface underneath it, trying as much as possible to make it perfectly parallel. Lets say the distance of the sensor and the flat surface would be 500mm. I would put the rubber sheet of say 4.1mm of thickness on the flat surface and now the distance measured would be 495.9mm. How feasible is that? Thanks in advance!

long microsecondsToCentimeters(long microseconds) {
  // The speed of sound is 340 m/s or 29 microseconds per centimeter.
  // The ping travels out and back, so to find the distance of the
  // object we take half of the distance travelled.
  return microseconds / 29 / 2;
}

5.8us per millimetre

0.58us per 0.1 millimetre

Do you think that a 62.5ns per instruction MicroController can handle this?

And if you had googled something like, oh, say, arduino hc-sr04 accuracy, you would have found that these things have nowhere near the accuracy or precision you apparently require.

Typical ultrasonic thickness gauges use a transducer that is in contact with the part to be measured.