How much concrete do I need for a slab?

To calculate concrete needed for a slab, multiply length × width × thickness. For a 10ft × 10ft × 4-inch slab, you need approximately 1.23 cubic yards. Our calculator automatically includes the 10% waste factor.

How many bags of concrete do I need calculator?

The number of bags depends on your slab size and bag weight. For example, an 80lb bag covers about 0.44 cubic yards. A 10×10×4 inch slab would need approximately 3 bags of 80lb concrete mix.

How to calculate cubic yards of concrete?

Convert all measurements to feet first. Then use: Cubic Yards = (Length × Width × Thickness in feet) ÷ 27. For inches, divide thickness by 12 to convert to feet before calculating.

What is the concrete calculator formula?

Basic formula: Volume = L × W × T. For imperial units: Cubic Yards = (Length ft × Width ft × Thickness in) ÷ 324. For metric: Cubic Meters = (Length m × Width m × Thickness cm) ÷ 100.

How much does concrete cost per yard?

Bagged concrete typically costs $6-8 per 80lb bag, covering about 0.44 cubic yards each. Ready-mix concrete costs $100-150 per cubic yard. Our calculator compares different bag sizes for the best value.

How to calculate concrete bags needed?

First calculate your volume in cubic yards, then divide by the coverage per bag. An 80lb bag covers 0.44 cu yd, 60lb covers 0.33 cu yd, and 40lb covers 0.22 cu yd. Always round up and add 10% extra.

How to calculate concrete for a slab?

Measure length, width, and thickness of your slab. Convert to consistent units (all feet or all meters). Multiply these three dimensions to get volume. Add 10% waste factor for material ordering.

How much concrete will I need calculator?

Our free calculator provides instant results for any rectangular slab. Simply enter your dimensions, and it calculates volume, bags needed, and total cost automatically. Works for both imperial and metric measurements.

How do you calculate yards of concrete?

To calculate concrete yards: (Length ft × Width ft × Depth ft) ÷ 27 = Cubic Yards. For depth in inches, convert to feet first by dividing by 12. Example: 12ft × 12ft × 4in = 12 × 12 × 0.33 ÷ 27 = 1.78 cubic yards.

What thickness should my concrete slab be?

Standard thicknesses: Sidewalks - 4 inches, Driveways - 4-6 inches, Garage floors - 4-6 inches, Basement floors - 4-8 inches. Thicker slabs provide more durability but require more concrete.

Should I include a waste factor?

Yes, always include 10-15% waste factor when ordering concrete. This accounts for spillage, over-excavation, and measurement variations. Our calculator automatically includes 10% waste factor in all calculations.

Can I use this for non-rectangular footings?

For irregular shapes, break them into rectangular sections and calculate each separately, then add the volumes together. For circular slabs, use our Circular Calculator tool available in the sidebar menu.

How accurate is this calculator for cost estimation?

Our calculator provides highly accurate cost estimates based on current market prices. The calculator uses real-time pricing data and factors in regional cost variations to deliver precise cost calculations for your concrete projects.

Can this calculator help me save money on concrete costs?

Yes! Our smart calculator compares different bag sizes and shows cost-per-unit breakdowns to help you identify the most cost-effective purchasing options. The calculator also prevents over-ordering by providing accurate calculations.

What factors affect concrete cost in the calculator?

The calculator considers multiple cost factors including bag sizes, regional pricing, quantity discounts, and delivery costs. Geographic location significantly impacts concrete cost, and our calculator adjusts pricing automatically.

How does the calculator compare costs between bag sizes?

Our calculator analyzes cost-per-cubic-yard for each bag size option, showing you the total project cost breakdown. The calculator highlights the most economical choice by comparing unit costs.

Is this calculator suitable for commercial cost estimating?

While our calculator provides professional-grade calculations suitable for many commercial projects, larger commercial cost estimates may require additional factors like labor costs and equipment costs.

Concrete Column Calculator

Calculate concrete volume, bags needed, and cost for round columns, cylinders, and circular pillars. Perfect for vertical concrete structures

Diameter (in)

Height (in)

Number of Columns

Enter total number of columns needed

Per Column Volume

0 cu yd

Total Volume Needed

0 cu yd

3D Shape Preview

Why Choose Our Concrete Column Calculator?

Professional-grade concrete column calculator for round columns, square piers, fence post holes, and cylindrical concrete structures.

Column & Post Hole Calculator

Calculate concrete for round columns, square piers, fence post holes, and cylindrical structures with precision.

Round & Square Columns

Supports circular columns (diameter) and square columns (width x depth) with accurate volume formulas for both shapes.

Fence Post Concrete Calculator

Perfect for fence post holes, deck posts, and mailbox posts. Calculate bags needed for 4x4, 6x6 post installations.

Concrete Bag Calculator

Shows how many bags of concrete needed (40lb, 60lb, 80lb) with cost comparison for post hole concrete projects.

Imperial & Metric Units

Calculate in feet/inches or meters/centimeters. Instant conversion for international concrete column projects.

Free & Easy to Use

No registration required. Free concrete column calculator for contractors, DIYers, and homeowners building fence posts or piers.

How to Calculate Concrete for Columns & Post Holes

Follow these simple steps to calculate concrete for round columns, square piers, fence post holes, and cylindrical structures.

Measure Column or Post Hole Dimensions

For round columns, measure diameter and height. For square columns, measure width, depth, and height. For post holes, measure hole diameter and depth.

Tip: For fence post holes, standard depth is 1/3 of post height plus 6 inches for gravel base.

Select Column Shape & Enter Dimensions

Choose between circular (round) or rectangular (square) column shape. Input your measurements in feet/inches or meters/centimeters.

Note: Most fence post holes are 8-12 inches diameter. Deck posts typically use 10-12 inch holes.

Review Concrete Volume & Bags Needed

Instantly see cubic yards needed and how many bags of concrete for your post holes or column project (40lb, 60lb, or 80lb bags).

Important: One 80lb bag typically fills 2-3 standard fence post holes (10" diameter × 24" deep).

Compare Bag Sizes & Costs

Compare concrete bag options to find the most cost-effective choice for your fence post or column concrete project.

Pro Tip: For multiple post holes, 80lb bags provide better value. For single posts, 60lb bags are easier to handle.

Column Concrete Calculation Formula

Round Column Formula:

Volume = π × (Diameter/2)² × Height

Square Column Formula:

Volume = Width × Depth × Height

Post Hole Concrete (Imperial):


                        Volume (cu yd) = 3.14 × (Diameter in/2)² × Depth in ÷ 46656

Common Post Hole Sizes:

• 4×4 fence post: 8-10" diameter × 24" deep
• 6×6 deck post: 12" diameter × 36" deep
• Mailbox post: 8" diameter × 24" deep
• Pergola column: 12-16" diameter × 36-48" deep

Frequently Asked Questions About Concrete Column Calculators

Common questions about calculating concrete for columns, post holes, fence posts, piers, and cylindrical concrete structures.

How to calculate concrete for columns?

To calculate concrete for a round column, use: Volume = π × (Diameter/2)² × Height. For square columns: Volume = Width × Depth × Height. Convert to cubic yards by dividing by 27 (for feet) or 46,656 (for inches). Our concrete column calculator automatically handles these formulas for both circular and rectangular columns with precision.

How much concrete for a post hole?

A standard 8-inch diameter × 24-inch deep post hole requires about 0.028 cubic yards (0.75 cubic feet) of concrete. A 10-inch × 24-inch hole needs 0.044 cubic yards. One 80lb bag typically fills 2-3 standard fence post holes. Use our post hole concrete calculator to determine exact amounts for your specific dimensions.

How much concrete do I need for fence posts?

For 4×4 fence posts in 8-10 inch diameter holes, you need 0.5-0.75 cubic feet per post. For 6×6 posts in 12-inch holes, plan 1.2-1.5 cubic feet each. A typical fence with 10 posts spaced 8 feet apart needs about 2-3 bags of 80lb concrete. Our fence post concrete calculator provides exact bag quantities for your project.

What is the formula for concrete column volume?

Round column formula: V = π × r² × h (where r = radius, h = height). Square column formula: V = w × d × h (where w = width, d = depth, h = height). For imperial units, divide result by 46,656 to get cubic yards. Our calculator applies the correct formula based on your selected column shape.

How to calculate concrete for round columns?

Measure the diameter and height of your round column. Use the formula: Volume = 3.14 × (Diameter/2)² × Height. For a 12-inch diameter × 8-foot tall column, you need approximately 0.7 cubic yards. Our round column calculator handles circular, cylindrical, and pier calculations with industry-standard precision.

How many bags of concrete for post holes?

One 80lb bag fills approximately 0.6 cubic feet, covering 2-3 standard 8-10 inch diameter × 24 inch deep post holes. For 12-inch diameter holes, plan 1 bag per 2 holes. A 60lb bag fills about 2 standard post holes. Use our bag calculator to determine exact quantities based on your hole size and depth.

What size post hole for a 4×4 post?

For 4×4 fence posts, dig a hole 8-10 inches in diameter. Depth should be 1/3 of post height plus 6 inches for gravel base. For an 8-foot tall fence, dig 30-36 inches deep (8 ft ÷ 3 = 2.67 ft, plus 6 inches). This provides proper stability and frost protection for fence posts.

How deep should concrete be for fence posts?

Fence post concrete depth should be at least 1/3 of the above-ground post height. For 6-foot fence posts, dig 24-30 inches deep. In frost-prone areas, go below the frost line (typically 36-48 inches). Add 4-6 inches of gravel for drainage before pouring concrete around the post for maximum stability.

How to calculate concrete for pier foundations?

Pier foundations are similar to round columns. Measure pier diameter and depth. For a 12-inch diameter × 4-foot deep pier: Volume = 3.14 × (6 inches)² × 48 inches ÷ 46,656 = 0.12 cubic yards. Our concrete pier calculator works perfectly for deck piers, building piers, and foundation piers with accurate volume calculations.

Can I use this calculator for circular columns?

Yes! Our calculator specifically supports circular (round) columns. Simply select "Circular" shape, enter your column diameter and height, and the calculator uses the cylindrical volume formula (π × r² × h) to provide precise concrete volume for round columns, pillars, and cylindrical piers.

How much concrete per fence post?

Each standard fence post (8-10 inch hole × 24 inches deep) requires approximately 0.75-1.0 cubic feet of concrete. For 10-12 fence posts, plan on 2-3 bags of 80lb concrete. Calculate your specific needs by multiplying the concrete per post by the total number of posts in your fence project.

What is the waste factor for column concrete?

For column and post hole concrete, include 5-10% waste factor. Post hole concrete typically has less waste than slabs, but account for spillage and variations in hole size. Our calculator can include waste factor automatically, ensuring you order sufficient concrete for your column or post project.

How to mix concrete for post holes?

For post holes, use standard concrete mix or fast-setting concrete. Mix ratio is typically 1 part cement, 2 parts sand, 3 parts gravel. Add water until consistency is thick but pourable. Fast-setting concrete hardens in 20-40 minutes, regular concrete needs 24-48 hours. Follow bag instructions for best results.

How long for concrete to cure in post holes?

Standard concrete in post holes reaches workable strength in 24-48 hours but full cure takes 28 days. Fast-setting concrete sets in 20-40 minutes and can support weight in 4 hours. Wait at least 24 hours before attaching fence panels or applying heavy loads to posts for optimal strength.

Should I use fast-setting concrete for posts?

Fast-setting concrete is excellent for fence posts and smaller column projects where quick turnaround is needed. It sets in 20-40 minutes, allowing faster project completion. For large structural columns or in hot weather, standard concrete provides more working time. Both types achieve similar final strength for post applications.

Column & Post Hole Calculation Guide

Essential knowledge for calculating concrete columns, post holes, fence posts, and cylindrical pier foundations.

Column & Post Measurement

• Measure diameter for round columns
• Measure width × depth for square columns
• Post hole depth = 1/3 post height + 6"
• Standard fence post hole: 8-10" diameter
• Deck post hole: 12" diameter minimum
• Always measure hole depth from ground level

Post Hole Specifications

Standard Sizes:

• 4×4 post: 8-10" diameter × 24" deep
• 6×6 post: 12" diameter × 36" deep
• Mailbox: 8" diameter × 24" deep

Volume Calculation:

• 10" × 24" hole = 0.04 cu yd
• 12" × 36" hole = 0.09 cu yd
• Pier 12" × 48" = 0.12 cu yd

Post Hole Bag Coverage

80lb bag: ~0.6 cu ft

Fills 2-3 standard post holes

60lb bag: ~0.45 cu ft

Fills 2 standard fence posts

Fast-setting: Same coverage

Sets in 20-40 minutes

Project Planning

• Order 10-15% extra concrete
• Schedule delivery for early morning
• Have tools ready before mixing
• Check weather forecast (no rain)
• Prepare sub-base and forms first
• Plan for immediate use of mixed concrete

Cost Considerations

• Bagged: $6-8 per 80lb bag
• Ready-mix: $100-150 per cubic yard
• Delivery fees: $50-100 typical
• Minimum orders may apply
• Weekend/overtime rates higher
• Compare total project cost, not just per-unit

Quality Tips

• Use proper water-to-cement ratio
• Avoid adding excess water
• Consolidate concrete to remove air
• Level and smooth surface properly
• Allow adequate curing time
• Protect from temperature extremes

Quick Reference: Common Column & Post Hole Sizes

Common column sizes showing concrete volume and bag requirements for different dimensions
Column/Post Type	Hole Size	Volume (cu yd)	80lb Bags
4×4 Fence Post	8" dia × 24" deep	0.028	1 bag per 3 posts
4×4 Fence Post	10" dia × 24" deep	0.044	1 bag per 2 posts
6×6 Deck Post	12" dia × 36" deep	0.094	1 bag per post
Round Column (12")	12" dia × 8' tall	0.698	2 bags
Pier Foundation	12" dia × 48" deep	0.125	1 bag per pier

* Based on standard concrete coverage: 80lb bag = ~0.6 cu ft. Add 4-6 inches gravel base below concrete.