A 70 ring gauge cigar is 27.8 mm thick, or 1.09 inches, wider than a full inch. Ring gauge is measured in sixty-fourths of an inch, so 70 means 70/64 across. To convert any ring gauge yourself, divide by 64 for inches or multiply by 0.397 for millimetres.
For reference: a 54 is 21.4 mm, a 60 is 23.8 mm, a 64 is a full inch at 25.4 mm, and a 70 is 27.8 mm.
Seventy sits past the gordo, in specialty big-ring territory. The proportions change the smoke: a large volume of filler burns under proportionally little wrapper, so the blend loses much of the wrapper’s spice and turns broad, cool and mellow next to the same tobacco at a 50. The draw is easy and the burn is slow, usually well past an hour and a half.
Two practical notes. A 70 will not fit most guillotine cutters, so plan on a wide-gauge cutter or a V-cut. And it is a lot of cigar to hold; if you like the idea of a big ring gauge but want something more manageable, a 60 is the usual starting point.