Below you can see the front-view size comparison of the Olympus TG-870 and Olympus E-M10 III. The Olympus TG-870 is clearly the smaller of the two cameras. Its body is 9mm narrower, 20 mm shorter and 22 mm thinner than the Olympus E-M10 III.
The chart below depicts how two cameras compare with average dimensions of the cameras in their class.