# Hydrostatic pressure - unit issue

Question asked by Stefano Tiburzi on Apr 16, 2020
Latest reply on Apr 17, 2020 by Ryan Dark

Hello to everyone.

Trying to better understand how non uniform pressure loads work, I built a simple box 1x1x1 cubic-meter (plus a little frame over it) to cointain water.

Total weight of the water, 9810 N (1 m3 x 1000 Kg/m3 x 9,81 m/s2, simple as that). With its base fixed, after defined a coordinate system, I inserted the equation for hydrostatic pressure: p(z) = 9810*z N/m2.

The box is 20 mm thick S235JR steel and basically it didn't appeared affected by the load, as it should be and the reaction force was exactly equal to the weight of the water.

But I noticed the little ruler above the equation for the pressure which set the unit lenght for the (x,y,z) and was set as "m" (meters). As the units for the model are "mm" (millimeters), I changed from ther former to the latter, not thinking it was such a big deal...

then I run the simulation again and the results were magnified a thousand times! Box deformed as the steel exceeded the yield strenght and the reaction force was 9810000 N!

If someone doesn't pay attention to this detail, the results can be misinterpreted! Did anyone else notice or have this issue? Can someone explain how this is possible?

Thank you very much!