2a- Calculating Volume of Concrete:

Picture 2.1 Sample Foundation Plan

I always start with column footings.

 We have to locate the Footing Schedule, or there should be a note specifying what  F4.0 footing is.

F4.0 - 4’-0”x4’-0”, 24” thick with #6@12”o.c. E.W. Bot.

Or  

Table 2.1 Footing Schedule

If you can’t find footing schedule or any note specifies size and reinforcing of the footings, you have to send question to Structural Engineer via RFI “Request for Information” form. Do not make any assumptions. Engineer has to give you the response for your RFI.

We want to calculate the volume of the concrete and weight of the rebar for each concrete element. Concrete trucks delivers the concrete by cubic yards. Each truck can get up to 10 cy or 11 cy concrete. We have to convert our calculations to cubic yardage of the concrete, so we know how many trucks we need to order from supplier.

This is 1 cubic foot. 

Picture 2.2 One Cubic feet

And this is 1 cubic yard

Picture 2.3 One Cubic yard has 27 cubic feet.

Let’s calculate volume of F4.0 footing

4’-0”x4’-0”x2’-0” = 32 cf 

Picture 2.4 F4 Footing has 32 cubic feet.

So now, we know how to convert cubic feet to cubic yard.

Just divide it to 27.

Count and color all the F4.0 footings. I use orange for column footings. Try to use

We have (6) F4.0 footings,

F4.0 = 4’-0”x4’-0”x2’-0” x (6) / 27 = 7.11 cy   

Important point is all the units has to be feet. You can’t use inches together feet. You have to convert inches to decimal feet.

Let’s say we have these footing schedule with F3.5 and F4.33x5.66

Table 2.2 Footing Schedule Example

How to convert inches to decimal feet?

Basically divide it to 12, because 1 feet has 12 inches.

6” (inches) = 6/12 = 0.5’ (feet)

1” =1/12= 0.083’ 

you can use 0.08 as an increment for each inch addition.

2” = 2/12 = 0.16 ‘which is approx. 0.83’ + 0.83’

3” = 3/12 = 0.25’ which is approx. 0.16’ + 0.83’

Don’t force yourself to remember all. You will become expert on this after couple estimates. For now, use this table below.

Table 2.3 Inch to Decimal conversion

Table 2.2 Footing Schedule Example Repeated

F3.5 is 3’-6” square footing,

Width and length from table above is 3’ + (6/12=0.5) = 3.5 ‘and thickness is 1’ + (6/12=0.5) = 1.5’

Assume we have (10) F3.5 footings,

F3.5 = 3.5’ x 3.5’ x 1.5’ x (10)/27 = 6.8 cy

F4.33x5.66 is 4’-4”x5’-8” rectangular footing,

Width is 4’ + (4/12=0.333) = 4.33’ and length is 5’+ (8/12=0.666) = 5.66’ and thickness is 1’ + (6/12=0.5) = 1.5’

Assume we have (8) F4.33x5.66 footings,

F4.33x5.66 = 4.33 x 5.66 x 1.5 x (8) /27 = 10.8 cy

And don’t worry about 1/8” ,1/4”, 5/16”, just round it up to next inches.

For example:

4’-1 1/8” use 4’-2” =4’+(2/12=0.16’) =4.16’, 

5’-2 ¾” use 5’-3” =5’+(3/12=0.25’) =5.25’,

1’-4 ½” use 1’-5” =1’+(5/12=0.41’) =1.41’,

For estimating purpose, we don’t need fractions of inches. But it is important when carpenter is building the job. And It is necessary for the estimator to learn all the fraction of inches.

Table 2.4 Inch to Decimal Conversion for Fractions

1/8” represents simply 1/8 of an inch, when you divide 1 by 8, answer is 0.125.

1/8” = 0.125”, answer is still inch not feet, we just convert fraction to decimals.

We still need to convert that to feet.

4’-1 1/8” = 4’ + (1.125”/12=0.094) =4.094’

5’-2 ¾” =5’+(2.75/12=0.229’) =5.229’

1’-4 ½” =1’+(4.5/12=0.375’) =1.375’

Let’s get back to our estimation,

So far, we estimated Column footings

F4.0 = 4’-0”x4’-0”x2’-0” x (6) / 27 = 7.11 cy  

And we color all the column footings to orange.

Picture 2.5 Sample Foundation Plan, Footings are already taken off.

Now, we calculate continuous footings. We have to look for detail or a note which gives us information about size and reinforcing of the footing.

This is our foundation detail,

Picture 2.6 Foundation Wall Detail

Continuous Footings = 116’x2’x1’/27=8.59 cy,

And paint continuous footings to brown,

Picture 2.7 Sample Foundation Plan, Continuous Footings And Column Footings Already Taken Off.

Top of wall elevation is 7’-8” from top of 4” slab. Our wall height is 7’-8” +4” =8’-0”

Walls = 116’x8’x1’/27=34.37 cy, 

and paint walls to green,

Picture 2.8 Sample Foundation Plan, All The Footings and Walls Already Taken Off

Written by Kamil Cabuk , MS

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