quote 4keys: "ht. Have you tested how big a piece you need for certain weight?
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Kind-of. But buoyancy is going to be determined by the weight of the object versus its volume (or, the volume of water it displaces). So it will be different for each object that you wish to float.
Even the 3" is overkill for this device. I sunk it in the kitchen sink a few times. The inReach has some buoyancy on its own, just not quite enough to stay afloat without some help.