How many cubic feet are in an 80 lb bag of concrete?

A typical 80 lb bag of premixed concrete yields about 0.6 cubic feet of finished concrete. This calculator uses that figure to estimate the number of bags required.

What if I am using 60 lb or 40 lb bags instead?

As a rule of thumb, multiply the 80 lb bag count by about 1.33 for 60 lb bags and by 2 for 40 lb bags. Always check the yield printed on the bag for precise conversions.

What waste percentage should I choose?

For clean, well‑formed trenches and experienced crews, 5% waste may be sufficient. For hand‑dug trenches, uneven subgrade, or challenging access, 10% or more may be appropriate. When in doubt, err on the high side.

Does this calculator handle pier footings, pads, or isolated spread footings?

It is optimized for continuous strip footings. For isolated pad footings or piers, you can treat each footing as its own small block (length × width × depth or circular volume), calculate its volume, and sum the results manually.

Does this tool tell me how much rebar I need or whether my footing meets code?

No. It estimates concrete volume only. Rebar spacing, bar sizes, footing depth, and width must follow engineered designs and local building codes. Consult a structural engineer or local building department for those requirements.

construction calculator

Concrete Footing Calculator

Estimate footing volume and 80 lb bags from length, width, and depth.

Results

Volume (cubic ft): 44.00
Volume (cubic yd): 1.63
80 lb bags (approx): 73.33

Overview

Continuous concrete footings carry the load of walls and structures into the soil, and running short on concrete halfway through a pour is a headache you want to avoid. This concrete footing calculator takes your footing length, width, depth, and a waste allowance to estimate cubic feet, cubic yards, and approximate 80 lb bag counts so you can size a ready‑mix order or DIY bag purchase with confidence.

How to use this calculator

Measure or obtain the total linear length of your footing run in feet, including any turns or continuous sections that will be poured together.
Enter the footing length and footing width in feet. Width is the thickness of the footing from one side to the other, perpendicular to the wall or load it will support.
Enter the planned footing depth in inches. This is the vertical thickness of the footing, not the full trench depth if you are below frost line—use the concrete height dimension.
Choose a waste allowance percentage to cover over‑excavation, spillage, and irregularities. Contractors often use 5–10% depending on trench quality and placement method.
Review the calculated cubic feet, cubic yards, and approximate 80 lb bag count. Round up to avoid short loads or extra trips to the store.
If you plan to use 60 lb or 40 lb bags, convert the 80 lb bag estimate by multiplying by the appropriate factor (for example, about 1.33 for 60 lb bags and 2 for 40 lb bags).

Inputs explained

Footing length (ft): The total linear length of the footing run you plan to pour, in feet. Include all continuous segments of the footing for this calculation; separate sections can be calculated separately and summed.
Footing width (ft): The designed width of the footing in feet. This is the dimension perpendicular to the wall or column being supported, typically specified on structural or foundation plans.
Depth (in): The thickness of the concrete footing in inches, measured from the top of the footing to its bottom. The calculator converts this value to feet to compute volume.
Waste allowance (%): An extra percentage applied to the theoretical volume to account for over‑excavation, form imperfections, spillage, and concrete left in chutes or on tools. Typical values range from 5–10%.

How it works

Footings are typically rectangular in cross‑section. The geometric volume of a continuous footing is simply length × width × depth. Because depth is usually measured in inches, the calculator first converts depth to feet (DepthFt = DepthInches ÷ 12).

It then computes the raw volume in cubic feet: VolumeFt³ = LengthFt × WidthFt × DepthFt. This represents the idealized volume of concrete if the trench or form is perfectly shaped and leveled.

To account for real‑world conditions—over‑excavation, uneven subgrade, spillage, and leftover concrete in chutes or mixers—the calculator applies a waste allowance percentage. The waste‑adjusted volume is VolumeWithWasteFt³ = VolumeFt³ × (1 + WastePercent ÷ 100).

For ready‑mix orders, the calculator converts the waste‑adjusted cubic feet to cubic yards by dividing by 27, since one cubic yard equals 27 cubic feet. This yardage is what you would discuss with the batch plant when ordering.

For bagged concrete, the calculator assumes an 80 lb bag yields roughly 0.6 cubic feet of mixed concrete. It estimates the number of 80 lb bags as Bags80lb ≈ VolumeWithWasteFt³ ÷ 0.6. You would typically round this up to the next whole bag or pallet.

Formula

DepthFt = DepthInches ÷ 12
VolumeFt³ = LengthFt × WidthFt × DepthFt
VolumeWithWasteFt³ = VolumeFt³ × (1 + WastePercent ÷ 100)
VolumeYd³ = VolumeWithWasteFt³ ÷ 27
Bags80lb ≈ VolumeWithWasteFt³ ÷ 0.6

When to use it

A homeowner or contractor estimating how many cubic yards of ready‑mix to order for a new foundation footing before calling the batch plant.
A DIY builder planning to mix footing concrete from bags and needing a ballpark number of 80 lb bags for a small addition or deck project.
A project manager comparing the material volume of several footing segments to check whether they can be placed in a single truck load or will require multiple deliveries.
A designer or estimator cross‑checking a structural engineer’s footing volume notes against their own quick calculations as a sanity check.

Tips & cautions

Use measurements from structural or foundation drawings when available; they will specify footing width and depth required for the soil conditions and loads.
Inspect trench quality before finalizing your waste allowance. Rough, over‑dug trenches or hand‑dug work in uneven soil usually require a higher waste percentage.
Round up your yardage and bag counts. It is usually less costly to have a small amount of surplus concrete than to schedule an emergency short load or perform a cold joint to finish a footing.
If you expect to pour multiple footings or pads in one session, consider combining their volumes to optimize truck loads and minimize partial deliveries.
The calculator assumes a uniform rectangular cross‑section and constant footing dimensions along the length. Step footings, varying widths, or haunches require segment‑by‑segment calculations.
It does not account for rebar layout, tie bars, anchor bolts, frost depth, or soil bearing capacity—those must follow engineered designs and local building codes.
Large pours using pumps, long chutes, or difficult access may experience higher waste than the simple percentages used here; adjust accordingly based on past experience.
All volumes are geometric approximations. Actual concrete yield can vary with mix design and placement practices.

Worked examples

20 ft × 2 ft footing at 12 in depth with 10% waste

LengthFt = 20; WidthFt = 2; DepthInches = 12.
DepthFt = 12 ÷ 12 = 1 ft.
VolumeFt³ = 20 × 2 × 1 = 40 ft³.
VolumeWithWasteFt³ = 40 × 1.10 = 44 ft³.
VolumeYd³ ≈ 44 ÷ 27 ≈ 1.63 cubic yards.
Bags80lb ≈ 44 ÷ 0.6 ≈ 73 bags (round up to 75 for convenience).

12 ft × 1.5 ft footing at 18 in depth with 5% waste

LengthFt = 12; WidthFt = 1.5; DepthInches = 18.
DepthFt = 18 ÷ 12 = 1.5 ft.
VolumeFt³ = 12 × 1.5 × 1.5 = 27 ft³.
VolumeWithWasteFt³ = 27 × 1.05 ≈ 28.35 ft³.
VolumeYd³ ≈ 28.35 ÷ 27 ≈ 1.05 cubic yards.
Bags80lb ≈ 28.35 ÷ 0.6 ≈ 47.25 → plan for 48–50 bags.

Multiple footing segments combined

If you have two separate footing runs (for example, 15 ft and 10 ft long) with the same width and depth, calculate each volume and sum them before applying waste.
Use the combined volume to plan a single truck load or batch of bags instead of sizing each run in isolation.

Deep dive

This concrete footing calculator helps you turn footing dimensions into realistic material quantities. By entering length, width, depth, and a waste allowance, you get cubic feet, cubic yards, and an approximate 80 lb bag count to size ready‑mix orders or bag purchases for continuous strip footings.

It’s useful for both contractors and serious DIYers who want to avoid mid‑pour surprises. With a clear volume estimate and waste buffer, you can discuss loads intelligently with your supplier, compare the cost of ready‑mix versus bagged concrete, and coordinate pours across multiple footing segments.

Because it focuses on volume and not structural design, you can use it alongside engineered plans and local codes to make sure the right amount of material is on site when you are ready to pour.

FAQs

How many cubic feet are in an 80 lb bag of concrete?: A typical 80 lb bag of premixed concrete yields about 0.6 cubic feet of finished concrete. This calculator uses that figure to estimate the number of bags required.
What if I am using 60 lb or 40 lb bags instead?: As a rule of thumb, multiply the 80 lb bag count by about 1.33 for 60 lb bags and by 2 for 40 lb bags. Always check the yield printed on the bag for precise conversions.
What waste percentage should I choose?: For clean, well‑formed trenches and experienced crews, 5% waste may be sufficient. For hand‑dug trenches, uneven subgrade, or challenging access, 10% or more may be appropriate. When in doubt, err on the high side.
Does this calculator handle pier footings, pads, or isolated spread footings?: It is optimized for continuous strip footings. For isolated pad footings or piers, you can treat each footing as its own small block (length × width × depth or circular volume), calculate its volume, and sum the results manually.
Does this tool tell me how much rebar I need or whether my footing meets code?: No. It estimates concrete volume only. Rebar spacing, bar sizes, footing depth, and width must follow engineered designs and local building codes. Consult a structural engineer or local building department for those requirements.

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This concrete footing calculator provides a geometric volume estimate and approximate bag counts based on user-supplied dimensions and waste factors. It does not constitute structural design guidance and does not account for soil conditions, frost depth, reinforcement, or code requirements. Always follow engineered plans and consult qualified professionals when designing and constructing footings.