How Many Bags of Concrete Do You Need? (Calculator + Charts)

How Many Bags of Concrete Do You Need?

The number of bags you need equals your total concrete volume divided by the yield of one bag. One 80-lb bag of pre-mixed concrete yields about 0.60 cubic feet, so it takes roughly 45 bags to make one cubic yard. Get your volume in cubic feet, pick a bag size, and divide.

That's the whole idea. Every bag count — for a slab, a footing, a fence post, or a sonotube — comes from the same four steps:

1. Measure the space the concrete will fill (length × width × thickness).
2. Convert everything to feet and multiply for cubic feet.
3. Divide the volume by the yield of your chosen bag.
4. Add 5–10% for waste and round up to the next whole bag.

Quick start: Skip the hand math with the Concrete Bag Calculator — enter your dimensions in any unit, choose 40, 50, 60, or 80 lb (or 20 kg) bags, and it returns the exact bag count with a waste buffer already applied.

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The One Formula for Bag Count

The core formula is simply volume divided by yield: a 30 ft³ pour using 0.60 ft³ bags needs 50 bags. Pre-mixed bags make this easy because the manufacturer already accounts for the air voids and bulking of the dry ingredients — the printed yield is finished, cured concrete.

Bags = Total Volume (ft³) ÷ Yield per Bag (ft³)

Here are the standard yields you'll see on the bag and the resulting count per cubic yard:

Bag Size	Yield per Bag	Bags per yd³ (27 ft³)
40 lb	0.30 ft³	90
50 lb	0.375 ft³	72
60 lb	0.45 ft³	60
80 lb	0.60 ft³	45
20 kg	0.28 ft³	95

Notice the formula uses your wet volume directly. You only bring in the 1.54 dry-volume factor when you're batching loose cement, sand, and aggregate yourself — not when you're buying pre-mixed bags. For that manual-batching path, see how to estimate bags of concrete for any project, which walks through both methods in full.

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How Many Bags Are in a Cubic Yard?

A cubic yard is 27 cubic feet, so the bags-per-yard count is just 27 divided by the bag's yield. For the common pre-mix sizes that's 45 bags of 80-lb, 60 bags of 60-lb, 72 bags of 50-lb, or 90 bags of 40-lb. This single conversion is the fastest sanity check on any estimate.

To Make 1 yd³	Bags Needed
40 lb bags	90
50 lb bags	72
60 lb bags	60
80 lb bags	45

Why does this matter so much? Because mixing 45 to 90 bags by hand for a single yard is a long, heavy day. Once you're ordering concrete by the yard, the question quickly stops being "how many bags" and starts being "should I even use bags." For the full lookup spanning 0.25 to 5.0 cubic yards across every bag size, see concrete bags per yard.

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Which Bag Size Should You Buy? (40 vs 60 vs 80 lb)

For most pours, 80-lb bags are the most efficient choice — they yield the most concrete per bag, so you carry and open the fewest. Drop to 40 or 50-lb bags only when the lighter weight matters: tight access, overhead work, or a small repair where one big bag is overkill.

Bag Size	Yield	Bags per yd³	Handling	Best For
40 lb	0.30 ft³	90	Lightest, easy to carry	Small repairs, setting a single post, tight spaces
50 lb	0.375 ft³	72	Light	Small pads, post setting, limited storage
60 lb	0.45 ft³	60	Moderate	Mid-size pads, steps, footings
80 lb	0.60 ft³	45	Heaviest (~80 lb each)	Slabs, footings, walls — fewest bags total

There's a real trade-off here. Fewer 80-lb bags means less opening and less trips to the mixer, but each one is a genuine lift. If you're working alone or above shoulder height, two 40-lb bags often beat one 80-lb bag for your back. For matching the right product — high-early-strength, fiber-reinforced, fast-setting — to the job, see choosing the right concrete mix bag.

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How Many Bags by Project Type

Different projects shape the concrete differently, but the math never changes: find the volume, divide by yield, add waste. Below is a quick answer for each common project, with a link to the full worked guide. All examples use 80-lb bags (0.60 ft³) before waste.

Slabs & Patios

A flat slab is length × width × thickness. A 10 ft × 10 ft patio at 4 inches holds about 33 ft³, or roughly 56 bags of 80-lb mix. Thickness is the lever — going from 4 to 6 inches adds 50% more bags. See how many bags of concrete for a slab for sizes from 8×8 up to driveways.

Footings

Footings are long, narrow trenches. A 20-ft run, 12 in wide × 12 in deep, holds 20 ft³ — about 34 bags of 80-lb. Footings often run past the point where bags make sense, so check the volume early. Full examples are in footing bags of concrete.

Fence Posts

A post hole is a cylinder minus the post. A 4-in post in a 10-in-wide hole, 2 ft deep needs roughly 1–2 bags per post. Multiply by your post count and you'll know whether to buy by the bag or the pallet. See fence post bags of concrete for hole-size charts.

Sonotubes & Round Columns

Round forms use the cylinder formula, π × radius² × height. A 12-in-diameter sonotube, 4 ft tall holds about 3.1 ft³ — close to 6 bags of 80-lb. Diameter drives this fast, since the radius is squared. Full per-tube counts live in sonotube bags of concrete.

Retaining Walls

Most segmental retaining walls use bags mainly for the footing or core fill. A typical poured footing runs about 1–2 bags per linear foot, depending on width and depth. Wall height and design drive the rest — see retaining wall bags of concrete.

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Worked Example: Bags for a 10 × 10 Patio

Let's run a full count for one of the most common DIY pours — a 10 ft × 10 ft patio slab at 4 inches thick, using 80-lb bags.

Given:

• Length = 10 ft
• Width = 10 ft
• Thickness = 4 in = 0.333 ft

Step-by-step:

1. Area = 10 × 10 = 100 ft²
2. Volume = 100 × 0.333 = 33.3 ft³
3. Bags = 33.3 ÷ 0.60 = 55.5 → 56 bags
4. Add 10% waste = 56 × 1.10 = 61.6 → order 62 bags

Cross-check via yards: 33.3 ft³ ÷ 27 = 1.23 yd³. At 45 bags per yard, 1.23 × 45 = 55.5 — the same answer. That 1.23 yards is also a flag: it's past the point where mixing 56–62 bags by hand stays practical, which brings up the next decision.

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Concrete Bag Cheat Sheet

The table below gives the 80-lb bag count for popular projects at typical dimensions, before waste. Add 5–10% and round up for your actual order.

Project	Dimensions	Volume (ft³)	80-lb Bags	Full Guide
Fence post hole	10-in dia × 2 ft deep	~0.9	2	Fence posts
Small landing pad	3 × 3 @ 4 in	3.0	5	Slabs
AC / shed pad	4 × 4 @ 4 in	5.3	9	Slabs
Sonotube column	12-in dia × 4 ft	3.1	6	Sonotubes
Footing run	10 ft × 12 in × 12 in	10.0	17	Footings
8 × 8 slab	8 × 8 @ 4 in	21.3	36	Slabs
10 × 10 slab	10 × 10 @ 4 in	33.3	56	Slabs
12 × 12 slab	12 × 12 @ 4 in	48.0	80	Slabs

Anything in the 40-plus-bag range (about one cubic yard) is where most people start pricing a ready-mix truck instead. For instant counts at your exact dimensions, the Concrete Bag Calculator does the rounding and waste math for you.

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How Much Waste Should You Add?

Always add 5–10% on top of your calculated bag count, then round up to the next whole bag. Use 10% for small DIY pours and rough subgrades, and 5% for large, well-prepared sites. Spillage, an uneven base, and the mix stuck to your tools all eat into the total.

The reasons the cushion is non-negotiable:

• Uneven subgrade — a base that dips even half an inch adds real volume across a slab.
• Spillage and stuck mix — every bag opened and every wheelbarrow load loses a little.
• No partial re-orders — a hardware run mid-pour means a stalled batch and a possible cold joint.

The pallet rule: A standard pallet holds about 42 bags of 80-lb mix — just under one cubic yard (42 × 0.60 = 25.2 ft³ = 0.93 yd³). If your count lands within a few bags of a full pallet, buy the whole pallet. Suppliers rarely discount partial pallets, and the extra bags become your waste buffer.

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When Should You Switch to Ready-Mix?

The practical dividing line is about 1 to 1.5 cubic yards — roughly 45 to 68 bags of 80-lb mix. Below that, bags mixed on site are usually cheaper and far more convenient. Above it, the labor of hauling, opening, and mixing dozens of bags by hand outweighs the savings, and a ready-mix truck wins.

Think about what 45 bags actually means: that's a ton and a half of material to lift twice, plus hours at the mixer keeping a consistent water ratio. A truck delivers 8–10 yards in one pour with no mixing at all. For the full crossover analysis and cost comparison, see ready-mix concrete: how many bags?.

Decision shortcut: Under ~½ yard (≈ 22 bags), use bags. Between ½ and 1 yard, weigh price against effort. Over 1 yard, order ready-mix.

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Frequently Asked Questions

How many bags of concrete do I need for a 10x10 slab?

A 10 ft × 10 ft slab at 4 inches thick holds about 33 cubic feet, which is 56 bags of 80-lb mix (or 74 of 60-lb, or 90 of 40-lb) before waste. Add 10% and order about 62 bags of 80-lb. That's 1.23 cubic yards — right at the ready-mix crossover.

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

It takes 45 bags of 80-lb concrete to make one cubic yard. Each 80-lb bag yields about 0.60 cubic feet, and a cubic yard is 27 cubic feet (27 ÷ 0.60 = 45). For 60-lb bags it's 60, for 50-lb it's 72, and for 40-lb it's 90 bags per yard.

How many bags of concrete do I need per fence post?

Most fence posts need 1 to 2 bags per hole. A standard 4-in post in a 10-in-wide hole dug 2 feet deep takes about 0.9 cubic feet of concrete — roughly two 80-lb bags after subtracting the post. Deeper or wider holes for gate and corner posts need more.

Is it cheaper to use bags or ready-mix concrete?

Bags are cheaper under about 1 cubic yard (45 bags of 80-lb); ready-mix wins above it. The crossover is driven by labor — mixing dozens of bags by hand costs hours, while a truck pours 8–10 yards at once. Small pads and posts favor bags; slabs and driveways favor ready-mix.

How many 60-lb bags of concrete make a yard?

You need 60 bags of 60-lb concrete to make one cubic yard. Each yields 0.45 cubic feet, and 27 ÷ 0.45 = 60. That's 15 more bags than the 80-lb size — more lifting and opening, but each bag is lighter to handle.

Should I buy 40-lb or 80-lb bags?

Choose 80-lb bags for the fewest bags and least handling on slabs and footings. Choose 40-lb bags when weight is the constraint — tight access, overhead work, working alone, or a small repair. An 80-lb bag yields double a 40-lb bag (0.60 vs 0.30 ft³), so you buy half as many.

How do I calculate bags for an odd or L-shaped pour?

Split the shape into rectangles and cylinders, calculate each volume separately, then add them. Divide the total cubic feet by your bag's yield. For circular forms use π × radius² × height; for rectangles use length × width × thickness. The Concrete Bag Calculator handles each shape instantly.

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Related Guides

• How to Estimate Bags of Concrete for Any Project
• Concrete Bags Per Yard — Full Reference Tables
• How Many Bags of Concrete for a Slab
• Footing Bags of Concrete
• Fence Post Bags of Concrete
• Sonotube Bags of Concrete
• Retaining Wall Bags of Concrete
• Ready-Mix Concrete — How Many Bags?

Visit Concrete Calculator Max for the full suite of concrete estimation tools and reference guides.

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Summary

Working out how many bags of concrete you need is one formula plus one conversion:

• Bags = Total Volume (ft³) ÷ Yield per Bag (ft³)
• Yields: 80 lb = 0.60 ft³, 60 lb = 0.45 ft³, 50 lb = 0.375 ft³, 40 lb = 0.30 ft³
• Per cubic yard: 45 (80 lb), 60 (60 lb), 72 (50 lb), or 90 (40 lb) bags
• Add 5–10% waste and round up to the next whole bag
• Over ~1 cubic yard (≈ 45 bags), switch to ready-mix

For a 10 × 10 patio at 4 inches, that's 56 bags of 80-lb calculated, about 62 ordered. Run your own numbers in seconds with the Concrete Bag Calculator.