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

A common rule of thumb is about 45 80 lb bags per cubic yard, but the exact number depends on the specific mix and manufacturer. Always verify coverage on the bag label and adjust your estimate accordingly.

Should I always add a waste factor to my concrete order?

Yes. It’s wise to order an extra 5–10% of concrete to account for spillage, over‑excavation, uneven subgrade, and finishing variations. Running short can be far more expensive and problematic than having a small amount left over.

Can I use this calculator for round footings or sonotubes?

This calculator assumes rectangular shapes. For round piers or sonotubes, compute the volume using the formula for a cylinder (πr²h), convert to cubic feet, then divide by 27 for yards or compare to bag yields. You can still use the yard and bag relationships shown here after computing the cylindrical volume.

Does this calculator handle multiple pours or stepped slabs?

Not in a single run. For stepped slabs, multiple elevations, or separate pads, run the calculator for each rectangular section and sum the volumes and bag counts manually or in a spreadsheet.

Does this tool ensure my slab meets code or structural requirements?

No. It only estimates concrete volume. Slab thickness, reinforcement, joint spacing, and mix design should be determined by local building codes, engineering requirements, and industry best practices.

construction calculator

Concrete Volume Calculator

Estimate cubic yards, cubic feet, and bag counts for slabs, footings, and post holes.

Results

Cubic yards: 2.96
Cubic feet: 80.00
80 lb bags: 133.33

Overview

Accurately sizing concrete orders is critical: too little concrete can leave you scrambling mid‑pour with cold joints and delays, while too much ties up cash and leaves you with extra material to dispose of. Whether you’re pouring a small patio, a shed slab, or footings for a deck, you need a reliable way to turn dimensions into cubic yards and bag counts.

This concrete volume calculator does that translation for you. By entering the length and width of a slab or footing in feet and the thickness in inches, it estimates the total volume in cubic feet and cubic yards. It also converts that yardage into an approximate number of 80 lb bags so you can decide between bagged mix and ready‑mix delivery and plan your order confidently.

How to use this calculator

Measure the length and width of the slab, footing, or pad in feet. For example, a small patio might be 20 feet long by 12 feet wide.
Measure or choose the thickness in inches. Typical residential slabs are often 4 inches thick; footings or structural elements may be thicker.
Enter the length, width, and thickness into the calculator. The tool converts thickness to feet, computes the volume in cubic feet, and then converts to cubic yards.
Review the cubic yards output as the basis for ready‑mix orders and the cubic feet output if you want to break the volume into smaller pours or forms.
Check the 80 lb bag count estimate if you plan to use bagged mix. Consider rounding up to the next whole bag and adding extra for waste and uneven subgrade.
If you are pouring multiple sections (for example, a slab plus separate footings), run the calculator for each and sum the volumes and bag counts.

Inputs explained

Length: The long dimension of the slab, footing, or pad in feet. Measure along the longest edge of the area you plan to pour. For multiple sections, calculate each separately.
Width: The short dimension of the slab, footing, or pad in feet. Together with length, this defines the rectangular footprint of the pour.
Thickness: The depth of the concrete in inches. Common slab thicknesses are 4–6 inches for residential applications, while footings, piers, and structural elements may be deeper. Ensure your thickness meets local code and structural requirements.

Outputs explained

Cubic yards: The total concrete volume expressed in cubic yards, which is how ready‑mix concrete is typically ordered. Use this figure to size truck deliveries and plan your pour.
Cubic feet: The total concrete volume expressed in cubic feet. This can be useful for smaller projects, for breaking work into sections, or for cross‑checking calculations.
80 lb bags: An approximate number of 80 lb pre‑mix concrete bags needed to match the calculated yardage, using a rule‑of‑thumb yield of about 45 bags per cubic yard. Always confirm coverage on your particular bagged mix.

How it works

You provide the footprint of your slab or footing as length and width in feet and the thickness (depth) in inches. We first convert the thickness from inches to feet by dividing by 12.

We compute the volume in cubic feet using the standard formula for a rectangular prism: Cubic feet = Length × Width × Thickness_in_feet.

To express volume in cubic yards, we divide cubic feet by 27, since one cubic yard is 27 cubic feet.

For bag counts, we multiply the cubic yards by an approximate factor of 45 bags per cubic yard for 80 lb pre‑mix. This reflects a common yield for many 80 lb concrete mixes, though you should always check the specific product’s coverage information.

The outputs show volume in both cubic feet and cubic yards along with the 80 lb bag estimate so you can compare bagged mix vs ready‑mix and ensure you order enough material.

Formula

Thickness_in_feet = Thickness_in_inches ÷ 12\nCubic feet = Length_ft × Width_ft × Thickness_in_feet\nCubic yards = Cubic feet ÷ 27\n80 lb bags ≈ Cubic yards × 45

When to use it

Estimating ready‑mix orders for driveways, patios, walkways, shed slabs, or garage floors based on slab dimensions and thickness.
Sizing bagged concrete purchases for smaller DIY projects such as pads for AC units, trash enclosures, garden sheds, or small retaining walls.
Comparing the material cost, labor, and logistics of mixing bags on site versus ordering a ready‑mix truck for projects near the threshold where either option might work.
Planning footing volumes for decks, pergolas, or simple foundations by approximating footings as rectangular sections (or breaking more complex shapes into rectangles).
Quickly ballparking how much concrete is needed when discussing project scope with clients, suppliers, or crew members.

Tips & cautions

Always add a waste factor—often 5–10%—to account for spillage, uneven ground, over‑excavation, and minor measurement errors. Running short of concrete during a pour is usually more costly than having a small surplus.
For irregular slabs or areas with thickened edges, grade beams, or trenches, break the shape into simple rectangles, calculate volume for each, and add them together. Use separate runs of the calculator if helpful.
Check the yield information on your specific bagged concrete product. Some mixes list coverage per bag in cubic feet; use that number instead of the generic 45 bags per yard rule when accuracy is important.
Verify that your slab thickness and reinforcement (rebar, wire mesh, fibers) meet local code and engineering requirements; this calculator focuses on plain volume only.
Consider site access and placement method (wheelbarrows, chutes, pumps) when deciding whether to use bagged mix or ready‑mix trucks—practical constraints can matter as much as pure volume.
Assumes a simple rectangular footprint with uniform thickness. Irregular shapes, slopes, thickened edges, and variable depths require segmenting the pour into smaller sections and summing volumes.
The bag‑per‑yard factor is an approximation; actual yields vary by product, mix design, compaction, and how accurately you measure water and mix ratios.
Does not account for reinforcement materials (rebar, mesh, anchors), sub‑base or gravel, or any admixtures you may need for the project.
Assumes a fixed slab thickness. In practice, forms, subgrade, and finishing can introduce variation in depth that may slightly increase the true volume required.
This tool does not replace detailed structural calculations or engineered plans; it is meant for material estimating only.

Worked examples

Example 1: 20×12 slab, 4" thick

Length = 20 ft; width = 12 ft; thickness = 4 in.
Thickness_in_feet = 4 ÷ 12 ≈ 0.333 ft.
Cubic feet = 20 × 12 × 0.333 ≈ 79.92 ft³ (about 80 ft³).
Cubic yards = 79.92 ÷ 27 ≈ 2.96 yd³.
80 lb bags ≈ 2.96 × 45 ≈ 133 bags (round up and add waste).

Example 2: 10×10 pad, 6" thick

Length = 10 ft; width = 10 ft; thickness = 6 in → 0.5 ft.
Cubic feet = 10 × 10 × 0.5 = 50 ft³.
Cubic yards = 50 ÷ 27 ≈ 1.85 yd³.
80 lb bags ≈ 1.85 × 45 ≈ 83 bags. Adding 10% for waste, you might plan around 90 bags or slightly more.

Example 3: Slab plus thickened edge

Main slab: 12×12 ft, 4 in thick → thickness 0.333 ft; volume ≈ 12 × 12 × 0.333 ≈ 47.9 ft³.
Thickened edge: approximate as a 1‑ft wide perimeter strip (roughly 12×1 ft on each side) at 12 in thick → additional volume calculated separately.
Run the calculator for each rectangular section and sum the cubic feet and yards to get a more accurate total.
By segmenting the slab this way, you capture extra concrete needed for structural edges and avoid under‑ordering.

Deep dive

Use this concrete volume calculator to convert slab and footing dimensions into cubic yards, cubic feet, and approximate 80 lb bag counts. Enter length, width, and thickness to size your concrete order before you schedule a pour.

Ideal for contractors and DIYers planning slabs, pads, and footings, the calculator helps you avoid under‑ordering or over‑ordering by turning simple measurements into practical yardage and bag estimates with a recommended waste buffer.

FAQs

How many 80 lb bags are in a cubic yard of concrete?: A common rule of thumb is about 45 80 lb bags per cubic yard, but the exact number depends on the specific mix and manufacturer. Always verify coverage on the bag label and adjust your estimate accordingly.
Should I always add a waste factor to my concrete order?: Yes. It’s wise to order an extra 5–10% of concrete to account for spillage, over‑excavation, uneven subgrade, and finishing variations. Running short can be far more expensive and problematic than having a small amount left over.
Can I use this calculator for round footings or sonotubes?: This calculator assumes rectangular shapes. For round piers or sonotubes, compute the volume using the formula for a cylinder (πr²h), convert to cubic feet, then divide by 27 for yards or compare to bag yields. You can still use the yard and bag relationships shown here after computing the cylindrical volume.
Does this calculator handle multiple pours or stepped slabs?: Not in a single run. For stepped slabs, multiple elevations, or separate pads, run the calculator for each rectangular section and sum the volumes and bag counts manually or in a spreadsheet.
Does this tool ensure my slab meets code or structural requirements?: No. It only estimates concrete volume. Slab thickness, reinforcement, joint spacing, and mix design should be determined by local building codes, engineering requirements, and industry best practices.

Related calculators

construction

Paint Coverage Calculator

Estimate gallons of paint needed based on wall area, coats, and coverage rate.

construction

Tile Calculator

Determine tile counts and total area including waste.

construction

Gravel Volume Calculator

Estimate cubic yards and tons of gravel required for driveways, pads, or drainage projects.

construction

Fence Calculator

Estimate the number of fence panels and posts required for a perimeter.

This concrete volume calculator estimates cubic footage, cubic yards, and approximate 80 lb bag counts based on user-entered dimensions and a simple rectangular volume formula. It does not account for complex shapes, extra depth at edges, reinforcement, subgrade conditions, or specific code and engineering requirements. Always verify measurements on site, include a reasonable waste factor, review product yield information, and consult with contractors, suppliers, or engineers before placing concrete orders for structural or safety-critical work.