A pocket penetrometer is a fantastic little invention which geotechnical engineers and technologists find very handy. It is a small handheld gauge which contains a telescoping rod which can be pushed into the soil. The distance the rod goes into the soil corresponds to a compressive strength on the dial.
Measurement of Soil
The pocket penetrometer measures the compressive strength of the soil. Most penetrometers available today contain units of tons/ft2 or kg/cm2, and the compressive strength is read directly from the gauge. Some common conversions are:
1 ton/ft2 = 2000 psf = 13.9 psi
1 kg/cm2 = 98.1 kPa
A pocket penetrometer is a primative instrument that is subject to many errors such as non-uniform soil. As a minimum, you should take a series of measurements in one area and average them. The penetrometer should not replace laboratory testing or field analysis, or be used to produce foundation design data.