concrete

[barbarian]

Originally Posted by Gottogo49

You obviously know a lot more about concrete than I do but why do you use 81 and 75 to divide by. 81 corresponds to 4" thick and 75 corresponds to 4.35" but why not just Length X Width X Thickness in ft divided by 27. You can always round up or just order 10% extra. Just wondering.

Just a quick easy way for us to quickly calculate a job that we are not physically looking at. Most jobs usually average 4" even if the forms are touching the ground on the exterior. If you knew how many times customers came up 1/4 yard short. Then a 1 yrd minimum delivery and a short load fee now added in because we had to deliver 2 partial loads cost about an extra $175 where an extra $30-50 from the start would've covered it more than easily. For example: 10 x 30 patio is 300sf. My calculation says (300/81= 3.7 yrds) (300/75=4yrds) or (10x30x.29167=1050/27= 3.24yrds). You might could try 3.5 yards if you are really concentrating on keeping it perfectly level, but usually 4yards would be the safe bet and waste a 1/3-1/4 yards or pour a little extra piece or something if your brain won't let you waste something you paid for. It is just too hard to use a calculation based upon perfection in the world of concrete and dirt work and definitely costly if you get it wrong.