Asteroids you can step off of vs. those you can't

I noticed in a few of the articles on Rosetta's flyby of the 21 Lutetia asteroid that some were not sure whether this asteroid was the type where one misstep could send you careening into space, or whether it had sufficient gravity to hold people to the surface. The answer is of course that with a diameter of 100 km it has more than enough gravity to hold people to the surface, and indeed it would be impossible to escape without a velocity of some 300 kph. But while calculating the surface gravity and escape velocity of a body isn't very complicated it still isn't one that can be done in one's head in the same way area, circumference and all the rest can, so I thought it would be helpful to come up with a quick chart of the surface gravity, escape velocity and surface area of asteroids at different diameters.

The calculation assumes a sphere, and while smaller asteroids are almost never perfectly spherical it's the only way to make a rough calculation. It also assumes an average density of 4 grams per cm³, and so keep in mind that this can vary a bit as well. I have also added equivalent regions or countries to the surface area in order to give a good idea of how much there is to explore.

You can see that it doesn't take much to have an asteroid where the escape velocity is greater than any slight misstep, and a diameter of 5 km is sufficient here, while by the time you get to a diameter of 15 km those on the surface are very secure. The asteroid 243 Ida has an escape velocity that varies depending on how far away you are from the centre, but even at the furthest tip it's still 52 kph and this can reach as high as 100 kph closer to the centre, so that asteroid is safe for human explorers as well.

Back to the chart: it goes up to 300 km and then straight to 4 Vesta (the most massive asteroid but not the largest; 2 Pallas is slightly larger), as once you reach 200 - 300 km it's easier to just look directly at the information for each asteroid as there aren't many left. Ceres, of course, is larger still though it is no longer considered to be just an asteroid.

Diameter	Surface gravity (% Earth)	Escape velocity	Surface area	Equivalent city/country
100 m	0.0006%	0.27 kph	31415 m2
500 m	0.0028%	1.3 kph	0.78 km2	Slightly more than Vatican City
1 km	0.0057%	2.7 kph	3.14 km2	Slightly more than Monaco
2 km	0.01%	5.4 kph	12.56 km2	Tokelau
3 km	0.017%	8 kph	28 km2	Macau
5 km	0.029%	13.5 kph	78 km2	Guernsey
10 km	0.057%	27 kph	314 km2	Malta
15 km	0.086%	40 kph	706 km2	Singapore
20 km	0.11%	54 kph	1256 km2	Hong Kong
25 km	0.14%	67 kph	1963 km2	Mauritius
30 km	0.17%	80 kph	2827 km2	Luxembourg
35 km	0.2%	94 kph	3848 km2	Cape Verde
40 km	0.23%	108 kph	5026 km2	Trinidad and Tobago
45 km	0.26%	121 kph	6361 km2	Palestinian Territories
50 km	0.29%	134 kph	7854 km2
60 km	0.34%	161 kph	11309 km2	Qatar
70 km	0.4%	188 kph	15393 km2	East Timor
80 km	0.46%	215 kph	20106 km2	Slovenia
90 km	0.51%	242 kph	25446 km2	Macedonia
100 km	0.57%	269 kph	31415 km2	Belgium
125 km	0.71%	336 kph	49087 km2	Slovakia
150 km	0.86%	404 kph	70685 km2	Ireland
175 km	1%	471 kph	96211 km2	South Korea
200 km	1.14%	538 kph	125 663 km2	North Korea
250 km	1.42%	672 kph	196 400km2	Segenal
300 km	1.7%	807 kph	282 740 km2	New Zealand
Vesta (529 km)	2.24%	1260 kph	840 000 km2	larger than Turkey