The Mass State Plane coordinate system is metric and may be converted to U.S. survey feet (its alternate system) by multiplying meters by the fraction 3937/1200.

U.S. survey feet may be converted to meters by multiplying U.S. survey feet by the fraction 1200/3937.

The common foot is a different unit of measurement, one-third of the Imperial standard yard, which is defined to be 0.9144 meters, exactly. Thus the (Imperial) foot is defined as 0.3048 meters, exactly.

If you are not working in meters you need to make absolutely sure you and everyone working on a survey's Mass State Plane coordinates are working in survey feet, not feet.

Discussion:

In 1959, the directors of the National Bureau of Standards and the United States Coast and Geodetic Survey agreed on a redefinition of the inch-centimeter relationship. This redefinition defined 1 inch as equal to 2.54 centimeters, exactly, or 1 foot as equal to 0.3048 meters, exactly.

However, their agreement stipulated that the older value for 1 meter equaling 39.37 inches, exactly, be retained for identifying the U.S. survey foot.

One of the reasons for this retention was that the State Plane Coordinate Systems, which are derived from the national geodetic control network, are based on the relationship of 1 meter equaling 39.37 inches, exactly.

The difference between these two values for the foot is very small, two parts per million, but not trivial in coordinate work. Fundamental survey units, such as rods, chains, statute miles, acres, sections, and townships, all depend on the relationship of 1 meter equaling 39.37 inches, exactly.