OK, after a visit to

wikipedia to remind myself how the math works, it seems that the energy needed to escape a body is given by

Energy = G * m1 * m2 / r,

Where G, m1, m2 are obvious, and r is (in this case) the radius of the planet(oid).

So, if we change my units from the previous post to SI, I get an energy input by jumping for a 180 lb athlete with a 4 ft vertical leap of ~ 1000 m2 kg /s2, (or N*m, whichever you prefer)

I was lazy and used a spreadsheet instead of working out the math directly, but though quick iteration, I get a limiting planet(oid) mass of ~4E14 kg, and a radius (at SG = 3) of a little over 3000 meters. Circumference is about 20000 meters, or about half of

**antoniseb**'s guess of 28 miles. So we're in the same ball park.

edited to add: feel free to check my math, as I didn't double check and I'm tired. I assumed a 120 kg astronaut + spacesuit.