Concrete Column Calculator

Concrete, bags, rebar cage and forms for round, square or rectangular columns and piers.

Project Details
Enter your measurements and requirements
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Results
Calculated estimates for your project
Concrete, with waste0.26 cu yd (0.20 m³)
Net volume6.28 cu ft (6.28 cu ft per column)
Cross-section113.1 sq in (0.785 sq ft)
Premix bags12 x 80 lb, or 16 x 60 lb, or 24 x 40 lb
Weight942 lb per column, 942 lb total
Vertical bars6 #4 at 9 ft 8 in (includes 20 in lap into the footing)
Steel ratio1.06% (inside the 1% to 8% range)
Ties13 #3 ties at 8 in spacing, 35 in each
Rebar total53 lb
Forms1 form tube, 8 ft
Total with bags$159.98
Total with ready-mix$256.98

Turn these numbers into a build plan.

  • 0.26 yd³ concrete
  • 12 80 lb bags
  • 53 lb rebar
Materials List
Recommended materials and quantities
80 lb premix bags (12)$78.00
Rebar (53 lb)$57.98
Form tubes (1)$24.00
Dashed line is the tie, 1.5 in in from the face; dots are the 6 vertical bars.

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Project plan · built from your numbers

Pour 1 concrete column

Form, reinforce and pour 1 12 in round column, 8 ft tall: 0.26 yd³ of concrete with waste, 6 #4 verticals and 13 #3 ties per column.

Materials
$160
Time
1 day plus cure
Level
Intermediate
5 steps 6 tools 5 materials
  1. 1

    Form and brace

    Set each form on the footing, plumb it on two faces and brace it from two directions so it cannot rack during the pour.

    • Forms plumb
    • Braces staked
    • Tops at the same elevation
  2. 2

    Set the cage

    Tie 6 verticals inside 13 ties at 8 in spacing, lap 20 in onto the footing dowels and hold 1.5 in of cover all round.

    • Cage tied
    • Lap length checked
    • Spacers on every face
  3. 3

    Pour

    Place concrete in lifts of about 2 ft, consolidating each one. Tap the forms to release trapped air.

    • Pour in lifts
    • Consolidate each lift
    • Strike off and set any post bases
01 · Your numbers
Concrete
0.26 yd³
80 lb bags
12
Rebar
53 lb
Est. cost
$160
02 · The plan

5 steps · 6 tools · 5 materials

2 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

Your plan is 60% built. Save it.

3/5

Pour 1 concrete column

Finished in 1 day plus cure · $160 DIY

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How the concrete column calculator works

  1. Find the cross-section. Round: 3.1416 x (diameter / 2) squared. Square: side x side. Rectangular: width x depth. Work in inches, then divide by 144 for square feet.
  2. Multiply by height and count. Square feet x height in feet x number of columns gives cubic feet. Divide by 27 for cubic yards.
  3. Add waste. Add 5 to 10% for spillage and form bulge, 15% for hand-mixed pours into tall forms.
  4. Convert to bags. Divide cubic feet by 0.60 for 80 lb bags, 0.45 for 60 lb or 0.30 for 40 lb. Above about 1 cubic yard, price ready-mix.
  5. Take off the rebar. At least 4 vertical bars in a square column and 6 in a round one, ties spaced no more than 16 bar diameters, 48 tie diameters or the smallest side, and 1.5 in of cover.

This tool gives volume and a material takeoff, not a structural design. Column size and steel for anything that carries a floor or roof come from an engineer. Pouring round tubes for deck piers? The sonotube calculator covers round form tubes and deck piers tube by tube. Need a pad under each column? Add a footing pad with the concrete footing calculator and its steel with the footing rebar calculator.

Concrete per foot of column height

SizeRound, cu ft / ftRound, 80 lb bags / ftSquare, cu ft / ftSquare, 80 lb bags / ft
6 in0.1960.330.2500.42
8 in0.3490.580.4440.74
10 in0.5450.910.6941.16
12 in0.7851.311.0001.67
14 in1.0691.781.3612.27
16 in1.3962.331.7782.96
18 in1.7672.952.2503.75
24 in3.1425.244.0006.67

Worked examples

JobConcrete with 10% waste80 lb bagsRebarForms
Four 12 in round porch columns, 8 ft1.02 cu yd47211 lb, ties at 8 in4 x 8 ft tubes
One 16 x 16 in garage column, 9 ft0.65 cu yd30114 lb, ties at 10 in2 plywood sheets
Ten 10 in deck piers, 4 ft0.89 cu yd40None (light pier)10 x 4 ft tubes

Column rebar rules

RuleValue
Minimum vertical bars4 in square or rectangular columns, 6 in round
Steel ratio1% to 8% of the gross cross-section
Tie spacingLeast of 16 bar diameters, 48 tie diameters or the smallest side
Tie size#3 for #10 verticals and smaller, #4 for larger
Cover1.5 in to the ties
Lap into footing dowelsAbout 40 bar diameters (20 in for #4)

Mix ratio and strength

Ratio (cement : sand : gravel)AboutUse
1:1.5:34000 psiDriveways, garage floors, structural footings (add air entrainment in freeze-thaw areas)
1:2:33500 psiPatios, sidewalks, steps
1:2:43000 psiSlabs, footings, fence and deck posts
1:2.5:52500 psiLight-duty pads, shed bases
1:3:62000 psiLean fill, mud slabs, under footings

Mixing your own? The concrete mix calculator covers mixing by ratio. For slabs around the columns use the concrete slab calculator, and for deck posts, size the footing first with the deck footing size calculator. Cure times and mix ratios are on the concrete cheat sheet.

Concrete column calculator FAQ

How much concrete does a 12-inch column need?

A 12 in round column is 0.785 cu ft per foot of height, so an 8 ft column is about 6.3 cu ft (0.23 cu yd). A 12 in square column holds 1 cu ft per foot, about 27% more.

How many 80 lb bags for a 12 inch column?

About 1.3 bags per foot of height for a 12 in round column, so 11 bags for 8 ft before waste and 12 with 10% added. A 12 in square column takes about 1.7 bags per foot.

How much concrete fits in a Sonotube?

A form tube holds the same as a round column of its inside diameter: about 0.35 cu ft per foot for 8 in, 0.79 for 12 in. For tube-by-tube deck pier counts, use the sonotube concrete calculator.

How much rebar in a concrete column?

Code columns carry at least 4 vertical bars (6 in a round column) making up 1% to 8% of the cross-section, tied with #3 ties for #10 bars and smaller. A 12 x 12 in column with 4 #5 bars is 0.86%, so it needs a size up or more bars.

Do concrete piers need rebar?

Structural piers and columns get a vertical cage doweled into the footing. Light deck piers often use one or two bars or none; follow your local code and the plans.

What is the difference between a column, a pier and a post footing?

A column stands above grade and carries a beam or roof. A pier is a short column, mostly below grade, that lifts a structure off the soil. A post footing is the pad or hole a wood post sits on. Size the pad under any of them with the concrete footing calculator.

What is the minimum size for a concrete column?

Most codes and engineers start structural columns at 8 to 10 in for residential work and 12 in when they carry a floor or roof beam. Anything load-bearing should be sized by an engineer.

Can I pour a column in one lift?

Short columns, yes. Tall ones should go in lifts of about 2 ft with consolidation between them, because fresh concrete pushes on the form like a liquid (about 150 lb per sq ft per foot of depth) and can blow out a weak form or leave voids.

How deep should a pier or post footing be?

Below the local frost line (often 12 to 48 in) and onto undisturbed soil. Include any bell or pad at the base in the height.

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