Concrete jobs are unforgiving: order too little and you get a cold joint halfway through a pour, order too much and you pay to haul it away. These calculators turn your measurements into cubic yards for a ready-mix order, or bag counts for 40, 60 and 80 lb mixes you blend yourself.
The same approach covers asphalt driveways (by the ton), block and brick walls (by the square foot), and retaining walls with their drainage stone. Each one includes a waste allowance, because forms are never perfectly square and subgrades are never perfectly flat.