An area 20ft x 34' is 680 square feet. 4 inches is 1/3 of a foot so cubic feet required is 680 x 1/3 = 226.7 cubic feet. There are 3x3x3 = 27 cubic ft in a cubic yard. Therefore cubic yards required = 226.7/27 = 8.4 cubic yards
1 cubic yard covers 324 square feet per inch of thickness, divide 324 by thickness in inches to get coverage, i.e. 4 inches thick would cover 324/4=81 square feet, 36 inches thick would cover (you guessed it) 9 square feet.
(10x16)/3 =53.3 cu ft 53.3/27=2 cu yards
30.81 cubic yards
20 feet x 20 ft x .3333 ft = 133.33 cubic feet / 27 cubic feet per yard = 4.94 cubic yards
That depends on how DEEP you want the concrete !
1 cubic yard covers 324 square feet per inch of thickness, divide 324 by thickness in inches to get coverage, i.e. 4 inches thick would cover 324/4=81 square feet, 36 inches thick would cover (you guessed it) 9 square feet.
8.25 cubic yards of concrete
Depends on how thick it is. At 4 inches thick, you would nee about 5.5 cubic yards adjusting for safety. At 6 inches, you'd need about 8 cubic yards. You can play with different thicknesses with the linked concrete pad calculator.
It depends on the thickness and the density. One ton should be about 15 cubic feet when compacted, so it would cover 30 square feet 6 inches thick or 45 square feet 4 inches thick or 60 square feet 3 inches thick. It would make a driveway four inches thick, 9 feet wide and 5 feet long or a footpath 3 inches thick, three feet wide and 20 feet long.
(10x16)/3 =53.3 cu ft 53.3/27=2 cu yards
30.81 cubic yards
20 feet x 20 ft x .3333 ft = 133.33 cubic feet / 27 cubic feet per yard = 4.94 cubic yards
That depends on how DEEP you want the concrete !
151/9 cubic yards for every 12 inches thick
An 80lb bag of concrete you can at your local home improvement store covers about 4 square foot at 2" thick. So you would need about 144 bags of 80lb concrete.
If you made a sidewalk about 2.5' wide it would be about 13' long.
I would guess about 70-80 bales