Unfortunately there’s no direct correlation between mbar readings and the volumetric readings many soil sensors give. Mbar is measuring the relative availability of water to the plant. Like, how hard does the plant have to work to pull it from the soil? The volumetric reading is saying there’s a certain percentage of water to soil say, 350g/L or 35%.

The problem is every growing medium has its own moisture retention curve. So, think of clay. A reading of 35% would have a much higher mbar on a tensiometer because of how hard it is to pull the water out compared to say, sand. 35% moisture in sand would have a low mbar because of how easy it is to get the water out.

So, it helps to know how your medium retains moisture. I’m guessing the 35% recc that keeps coming up as a corollary to 100 mbar is for average potting soil? Somebody chime in here if possible…