4.22g / 1cm³
0.0093035074564 lbs/ 1cm³ - First i convert the g to lbs
1cm³ = 0.032808399³ft - I took the equivalent of 1cm to 1ft which is 0.032808399
1cm³ = 0.000035314666882523470745199ft³ - then I cubed that equivalent
0.0093035074564 lbs / 0.000035314666882523470745199ft³ now it's in lbs per ft³ in crazy decimals so you divide it with a calculator (if it fits that many digits)
= 263.45lbs/ft³