How much concrete do I need for a slab?

Multiply length (ft) × width (ft) × thickness (ft) to get cubic feet, then divide by 27 for cubic yards. A 10 ft × 10 ft pad at 4 inches thick (0.33 ft) equals 33.3 cubic feet, or about 1.23 cubic yards. The calculator handles the conversion automatically — enter your dimensions in the Slab section and the totals update instantly. Always add 5–10% for waste and overage before placing your order.

How do I calculate concrete for a round hole?

The formula is V = π × radius² × depth. Enter the hole diameter in inches and the depth in feet in the Hole/Pier section — the calculator converts both into cubic yards for you. A 12-inch diameter hole at 4 feet deep holds about 0.13 cubic yards. For multiple holes at the same size, enter the quantity and the total scales automatically.

How many 80 lb bags of concrete are in a cubic yard?

One 80 lb bag yields approximately 0.6 cubic feet of mixed concrete, so one cubic yard (27 cubic feet) requires about 45 bags. Our calculator uses 45–50 bags per cubic yard as a conservative planning estimate. Always round up — you can return unopened bags, but you can't add concrete after a pour has started.

How many 60 lb bags of concrete are in a cubic yard?

A 60 lb bag yields about 0.45 cubic feet, so one cubic yard requires roughly 60 bags. For small projects under a quarter cubic yard, 60 lb bags are manageable to mix by hand. For anything larger, 80 lb bags or ready-mix delivery is faster and more cost-effective per cubic foot.

How much dirt comes out of a post hole?

A 12-inch diameter hole dug 4 feet deep removes about 3.14 cubic feet (0.12 cubic yards) of in-place soil. Factor in 20–30% swell — soil expands when excavated — and you are planning for roughly 0.14–0.15 cubic yards of loose spoil per hole. On a project with 20 identical holes, that is about 3 cubic yards of material that needs to go somewhere. Use the calculator's spoil estimates to plan truck loads before you start.

Should I order extra concrete?

Yes — always plan on 5–10% more than your calculated total. Real holes are never perfectly round, forms are not always level, and soil conditions vary. Spillage, over-excavation, and partial-bag leftovers are normal on every job. Running short mid-pour means stopping, mixing more, and risking a cold joint — a structural problem. Returning an extra bag or two is easy. Round up.

Does a pole or post in the hole reduce the concrete needed?

Technically yes, but rarely enough to change your order. A 4-inch round post displaces only about 5–10% of the concrete in a typical 12-inch hole. Experienced contractors do not reduce their order based on pole volume — the overage is your buffer against irregular hole shapes and spillage. Order for the full hole volume and let the post displace whatever it displaces.

How do I estimate concrete for fence posts?

Enter each post hole diameter and depth in the Hole/Pier section. A standard residential fence post typically uses a 10–12 inch diameter hole, 2.5–3 feet deep. If all your holes are the same size, enter the diameter, depth, and total quantity — the calculator sums them into one cubic yard total and gives you a bag count. Use the Slab section to add a continuous footer or base pad if needed.

How do I estimate concrete for sign foundations or bollards?

Sign and bollard foundations are typically drilled wider and deeper than standard post holes — often 18–36 inches in diameter and 4–10 feet deep. Enter the diameter in inches and depth in feet in the Hole/Pier section. For foundations with an above-grade concrete collar or base, use the above-grade base toggle to add that volume separately. For multi-sign projects with different hole sizes, add a row for each group.

What is the difference between cubic feet and cubic yards?

Cubic feet is the natural unit when you measure with a tape measure — multiply length × width × height in feet and you get cubic feet. Cubic yards is what ready-mix suppliers, haulers, and contractors use for ordering and pricing. One cubic yard equals 27 cubic feet. The calculator always converts your foot-and-inch inputs to cubic yards automatically, so you always get results in the unit you order by.

Field Planning Tool

Concrete Volume Calculator for Slabs, Posts, and Dirt Removal

Free concrete calculator for slabs, post holes, piers, and dirt removal. Enter your dimensions and get cubic yards, bag counts, and spoil estimates instantly — no formulas needed.

Drill Spoil VolumeHole & Slab ConcreteField ConversionsMulti-Group Projects

Drill Spoil Volume

Estimate total excavated material in cubic yards to plan for haul-off or on-site disposal.

Hole & Slab Concrete

Calculate concrete for drilled holes, above-grade bases, and flat slabs — all in one place.

Field Conversions

Convert totals to 80 lb bags, 60 lb bags, and ready-mix cubic yards for ordering.

Multi-Group Projects

Add multiple hole groups and slabs with different sizes — grand total auto-calculates.

Enter Your Project

Hole & Slab Calculator

Enter hole or slab dimensions — all values update live. Add multiple groups for projects with different sizes. A combined concrete total and bag count appear automatically at the bottom.

Hole / Pier Concrete

Hole Group 1

Description (optional)

Diameter (in)

Depth (ft)

Qty of Holes

Pole set in concrete

Above-grade concrete base

Concrete Slab

Label	Length (ft)	Width (ft)	Thickness (in)	Qty	Result (yd³)
					—

Estimating Assumptions

Pickup truck

≈ 2 yd³

Dump truck

≈ 10 yd³

50 lb bags / yd³

≈ 90 bags

Ready-mix truck

≈ 10 yd³

These are rough planning estimates. Actual truck capacities and bag yields vary. Concrete estimates do not account for waste or over-pour. Verify all quantities with your supplier before ordering.

Installing a Sign or Pole?

Use our Sign Foundation Calculator to estimate wind load, hole size, and concrete for freestanding signs — pole signs, pylon signs, and monument bases.

Open Sign Foundation Calculator →

The Math Behind the Tool

How to Calculate Concrete Volume

This concrete volume calculator answers the most common job-site question — “how much concrete do I need?” — for slabs, post holes, piers, and small foundations. It uses the same formulas contractors apply on site, and converts all results to cubic yards automatically.

Concrete Slab Calculator Formula

Slab volume = Length × Width × Thickness. The concrete slab calculator converts thickness from inches to feet, multiplies the three dimensions, then divides by 27 to get cubic yards. Bag counts for 80 lb and 60 lb bags are calculated and displayed alongside.

Example:A 10 ft × 10 ft pad at 4 in thick = 33.3 cubic feet, or about 1.2 cubic yards — and roughly 54 bags at 80 lb each.

Slab volume (ft³) = length × width × (thickness ÷ 12)
Cubic yards = cubic feet ÷ 27
The tool converts and rounds automatically — enter raw measurements

Round Hole and Pier Concrete Formula

Hole volume = π × radius² × depth. This post hole concrete calculator accepts diameter in inches and depth in feet, then converts to cubic yards in one step. It works as a drilled pier calculator, sign foundation calculator, and pole footing calculator — the shape is the same regardless of what goes in the hole.

Enter diameter in inches — radius is calculated internally
Depth in feet — the tool handles the unit conversion
Works for auger hole volume, drilled pier, bollard footings, and sign foundations

Cubic Feet vs. Cubic Yards

Cubic feet is the natural result when you measure in feet and inches — multiply length × width × height and you get cubic feet. Cubic yards is what ready-mix suppliers, haulers, and concrete contractors use for ordering and pricing. This cubic yard concrete calculator always presents results in the unit you order by.

1 cubic yard = 27 cubic feet — the only conversion you need to remember
Cubic feet = raw measurement; cubic yards = ordering unit
Calculator converts automatically — enter feet and inches, get cubic yards

Why You Should Order a Little Extra

Experienced contractors almost universally add 5–10% to their calculated concrete volume before ordering. Holes are never perfectly round, forms are rarely perfectly level, and conditions on the day of the pour always introduce small variables that add up.

Over-excavation, rough hole walls, and soil collapse add volume
Spillage and partial bags are normal on every job
Returning an extra bag is easy — running short mid-pour is a structural problem

Project Types

Common Projects This Concrete Calculator Handles

Built for quick homeowner estimates and daily contractor work alike.

Posts & Piers

Fence post holes
Gate and corner posts
Deck footings and pier pads
Pergola posts and patio cover footings
Mailbox posts with concrete bases
Basketball hoop footings

Slabs & Pads

Small concrete slabs and walkways
Shed pads and carport slabs
AC and equipment pads
RV pads and parking pads
Generator and utility bases

Signs, Bollards & Poles

Bollard footings and pier foundations
Sign foundations — commercial and monument
Light pole foundations
Parking lot poles and bases
Flagpole footings

Excavation & Dirt Removal

Dirt removal planning for drilled holes
Spoil estimation for slab excavation
Retaining wall footings
Step-down footings
Trench spoil volume

Spoil Planning

Dirt Removal Calculator and Spoil Estimates

When drilling post holes or excavating for a slab, the dirt also needs to go somewhere. This spoil removal calculator estimates both in-ground volume and loose spoil volume so you can plan truck loads and hauling before work starts.

In-Place Soil vs. Loose Spoil

The excavation volume calculator first determines in-place soil volume from your hole or slab dimensions. Once excavated, that same soil swells — loose spoil typically runs 10–30% higher in volume than in-ground measurements, depending on soil type and moisture content.

In-place volume = exact hole or slab dimensions
Loose spoil volume = in-place volume × 1.1 to 1.3 (swell factor)
Use loose spoil volume for truck load and hauling estimates

Cubic Yards to Truck Loads

These are rule-of-thumb estimates for planning purposes only — not guarantees. Actual hauling capacity depends on soil density, moisture, road weight limits, and truck configuration.

Full-size pickup

0.5–1.0 yd³

Varies by bed size and weight limits

Single-axle dump

5–7 yd³

Per load, depending on material weight

Tandem dump truck

10–14 yd³

Per load, standard commercial hauling

Formula:Estimated Loads = Total Spoil Volume (yd³) ÷ Truck Capacity (yd³ per load)

Hauling Considerations

Actual capacity depends on soil density, moisture, road weight limits, and truck type
Clay, wet soil, and concrete spoils are heavier and reduce safe load capacity
Always confirm load counts and pricing with your hauling provider before scheduling

Common Questions

Concrete Calculator FAQs

Built For

Who This Concrete Calculator Helps

HomeownersPlanning DIY slabs, pads, and posts

Fence InstallersPost setting crews and gate contractors

Sign ContractorsSign installation and foundation drilling

General ContractorsConstruction managers and GC crews

Concrete ContractorsFlatwork crews and concrete finishers

Property ManagersSmall repairs, pads, and replacements

LandscapersPergolas, mailboxes, and site furnishings

Bollard InstallersDrilled piers and auger hole volume

Pole ContractorsLight poles, flagpoles, and parking lot bases

Whether you pour from bags, order by the cubic yard, or just need a quick dirt removal estimate — this tool gives you fast, contractor-grade numbers.

Actual concrete and dirt volumes can vary due to over-excavation, uneven hole shapes, soil conditions, spillage, and waste. Hollow poles and posts usually do not reduce concrete needs enough to change your order. Always confirm final quantities on site and with your concrete supplier.

Related Services

Need help drilling fence post holes?Fence Post Drilling Services →Planning a new sign or pole?Sign Foundation Drilling Services →Installing bollards or barriers?Bollard Installation Services →Ready to schedule a pour?Concrete Pouring Services →Too much spoil to handle yourself?Dirt Removal Services →Need a quote for your project?Request a Quote →

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Use the calculator above to estimate your volumes, then get a fast quote from our team. Central Texas foundation drilling — sign posts, bollards, piers, and concrete work.

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