If each side is 0.5m the footprint is 0.5 x 0.5 = 0.25 square metres.
The limit is 4000N/square metre so the max load over 0.25 square metres is 4000 x 0.25 = 1000N.
If g = 10m/s2 there are 10N in a kg so the max force of 1000N equates to 100kg