Gravel is bought in cubic quantities, or by weight.
You ask "to fill" but you only give a square measure. The volume of gravel required wil depends on the depth you wish the gravel to be.
To fill 81 square metres to a depth of 5 cm would require 4.05 cubic metres of material.
500 m2 = 775,001.55 inches squared.
it depends how thickly you lay it.
about 71 cubic metres of gravel i think
16 cubic yards
Surface area is the sum of the areas of all the surfaces of an object. When you add units, they stay the same. Since you are adding, let's say, meters squared and meters squared and meters squared, your unit is still meters squared. Volume is a measure of how much space is inside an object. To find volume, you must multiply length, width, and height. In our example, that would be meters x meters x meters. When you multiply units, they multiply to each other. So, we get meters cubed, or meters^3.
100 meters squared
500 m2 = 775,001.55 inches squared.
it depends how thickly you lay it.
unit of area
about 71 cubic metres of gravel i think
4,219.5 square feet.
17.65 meters squared
2.438 2.438
Four square meters is 43.1 square feet.
16 cubic yards
471 (square meters) = 5,069.80181 square feet.
85002 is 8500 x 8500 which is: 72250000