Calculating the amount concrete of a rectangle
Length * Width * Depth / 27 = Cubic Yards
I usually add 10% to my order so I don't run short
To calculate concrete for patio that is 10 ft x 10 ft and 5 inches thick
Divide the number of inches 5 by 12
5 / 12 = .42 hold that number
Calculate the area: 10' * 10' = 100 sq ft
Now calculate cubic feet: 100 * .42 = 42
Now calculate cubic yards: 42 / 27 = 1.6 cubic yards
So I don't run short now add 10%: 1.6 * 1.1 = 1.76 cubic yards
To calculate concrete for patio that is 10 ft x 10 ft and 4 inches thick
10' * 10' = 100 sq ft
100 * .33 = 33 cu. ft.
33 / 27 = 1.2 cubic yards
1.2 * 1.1 = 1.32 cubic yards
Calculating the amount concrete of a cylinder
I use 3.14 for pi
To calculate the amount of concrete for hole 8" wide and 36 " deep the formula would be
Volume = pi * (r * r) * Height
Volume = 3.14 * (4" * 4") * 36"
Volume = 3.14 * 16" * 36"
Volume = 50.24 * 36"
Volume = 1,808.64 cubic inches
Convert to cubic feet
1,808.64 / 1,728 = 1.047 cu. ft.
Volume = 1.047 cubic feet
Convert to cubic yard
1.047 / 27 = 0.039 cu. yd.
Convert to 60lb bags concrete
0.039 * 3600 = 140.4
140.4 / 60 = 2.34 60lb bags concrete
For 80lb bags the calculation would be
140.4 / 80 =1.75 80lb bags concrete
More information about calculating bag in at the bottom of the page
Things to remember about the ordering of concrete
Different method of buying concrete
- Most concrete or ready-mix companies have 3 yards minimum order. Each companies minimum order can vary.
- Concrete can be ordered in 1/4 yd units
- For outside area like sidewalks and driveways Be sure your concrete is air-entrained to improve resistance to freezing.
- Stand-by-time for the truck is expensive, about $1 per minute, keep that in mind. You get roughly 6 minutes per yard to get the concrete off the truck after that you'll pay for stand-by-time.
- Calling around can save you money.
- Call and arrange your order ahead of time Some areas can be very busy and the companies may be booked up.
- The concrete truck: through a ready-mix company is economical for orders more than 3 yards in most cases. Above there are tips on ordering concrete through ready mix companies.
- Metered concrete service: For orders less than 2 yards you can use a metered concrete service. This truck come to your job with the materials stored in separate bins. The water is added as the concrete leaves the truck leaving little to no waste. This way you pay for what you use.
- For orders between 2 and 3 yards call both the ready-mix and metered and check their prices. It may be cheaper to buy a 3 yard minimum ever if you only need 2 yards. Call around.
- The trailer: One alterative to buying small amounts of concrete, one yard or less, is a trailer. This way is cheaper because you haul the concrete yourself. The company will rent you the trailer, fill it with concrete, and you haul it to your job. You will need a good size pickup because concrete is heavy, about 2 tons per yard.
- By the bag: The last method of buying concrete is by the bag. It can be inexpensive compared to a ready-mix company, but it is allot of work. I use 60lb bags as opposed to 80lb bags because they are easier to handle.
- With 60lbs bags, you will need 60 bags for 1 cubic yard of concrete
- 30 bags for 1/2 cubic yard
- 15 for a 1/4 cubic yard.
- With the 80lb bag will need 45 bags for 1 cubic yard
- 23 bags for 1/2 cubic yard
- 12 bag for 1/4 cubic yard.
There is 3600 dry pounds of concrete mix in a yard of concrete. So divide 3600 by the yardage of concrete needed. Then divide that answer by the weight of the bag. For example if you need a 1/4 yard of concrete and you have 90lb bags the formula would be:
Multiply by 3600 by the decimal of your yardage - 1/4 yd = .25
3600 * .25 = 900
divide the answer by the weight of the bag
900 / 90 = 10 bags
If the bags weighed 65 lbs
900 / 65 = 13.8 bags
If you have a question about anything dealing with what I have covered on this page or questions about concrete in general, please feel free to contact me by email
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