Concrete Bag Calculator
How many bags of concrete do you need? Compare 40, 60 and 80 lb or 20, 25 and 30 kg bags, total weight and cost — with the math shown.
- Free
- No sign-up
- Formula shown
- US & metric
Your estimate
80 lb bags needed
10 bags
- Concrete volume (incl. waste)
- 5.87 cu ft (0.22 cu yd)
- Total weight
- 800 lb
- 40 lb bags
- 20
- 50 lb bags
- 16
- 60 lb bags
- 14
Show the math
- Volume before waste = 5.33 cu ft
- × (1 + 10%) = 5.87 cu ft
- ÷ yield per bag 0.6 cu ft = 9.78 → 10 bags
Shopping list & cost
| Item | Spec | Qty | Cost |
|---|---|---|---|
| Premix concrete | 80 lb bag | 10 bags | — |
Prices are what you enter under Advanced options. Estimates only — check stock and pricing with your supplier.
Quick answer One cubic yard (27 cu ft) of concrete takes 45 bags of 80 lb premix (about 0.6 cu ft each), 60 × 60 lb or 90 × 40 lb bags. One cubic meter takes roughly 107 bags of 20 kg mix at a typical 9.4 L yield. Add 5–10% for waste and check the yield printed on your bag.
Diagram
How to use this calculator
- Choose whether you know the dimensions or already have a volume (for example from the slab calculator).
- Pick the bag size you can actually lift and carry — 80 lb (36 kg) bags are cheaper per yard but heavy.
- Keep 10% waste for post holes and small pours; irregular holes swallow more than you expect.
- Compare bag counts across sizes in the results to see which is cheapest at your store.
Method & assumptions
Bags = Volume × (1 + waste %) ÷ yield per bag, rounded up Total weight = bags × bag weight
- Volume
- cu ft (Imperial) or m³ (Metric)
- Yield per bag
- 40 lb ≈ 0.30 cu ft, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60; 20 kg ≈ 9.4 L, 25 kg ≈ 11.7 L, 30 kg ≈ 14 L (typical)
Assumptions & limits
- Yields are typical for standard premix; read your bag label and override the volume if different.
- Post-hole and fast-setting mixes often yield less per bag.
- Weight shown is dry bag weight; add water separately.
Rounding: purchase quantities are always rounded up to whole bags, boxes, sheets or bundles. See our methodology.
Worked examples
Imperial: 4 fence posts, 10 in holes 30 in deep
- Hole volume = π × (10 ÷ 2)² × 30 = 2,356 cu in each = 1.36 cu ft
- Minus the 4×4 post (3.5 × 3.5 × 30 = 368 cu in): 1.15 cu ft each, 4.6 cu ft total
- With 10% waste: 5.06 cu ft ÷ 0.45 = 11.2 → 12 × 60 lb bags
Metric: 0.15 m³ of concrete
- 0.15 × 1.10 = 0.165 m³
- 0.165 ÷ 0.0094 = 17.6 → 18 × 20 kg bags (360 kg)
In depth: concrete bags planning notes
Why bag yield is the number to check
Every bag of premix states a yield — the volume of finished concrete it makes once water is added. Typical values are about 0.30 cu ft for a 40 lb bag, 0.45 cu ft for 60 lb and 0.60 cu ft for 80 lb, and around 9–14 liters for 20–30 kg bags in metric markets. Fast-setting, high-strength and fiber-reinforced mixes often yield slightly less, so the label on the bag you are actually buying beats any default. Enter it in Advanced options and the count updates instantly.
The difference is not trivial. Fifty bags at 0.60 cu ft make 30 cu ft; at 0.56 cu ft they make 28 cu ft — a shortfall of three or four bags on a single afternoon job. When you are close to a round number, buy one or two extra bags; unopened bags are often returnable, and running short halfway through a pour leaves a cold joint.
Choosing a bag size
Bigger bags are usually cheaper per cubic foot and mean fewer bags to open, but an 80 lb (36 kg) bag is heavy to lift into a wheelbarrow or mixer repeatedly. Many people mix 60 lb or 20–25 kg bags for comfort, especially on post holes where only a few bags go into each hole. The comparison table shows the count, weight and cost for each size so you can pick on price and on what your back will tolerate.
For setting posts, consider the hole rather than the post: concrete fills the cylinder minus the post, and holes are rarely perfectly round. The fence calculator works this out per hole. For small repairs, a single bag of a fast-setting mix is often enough; check the working time on the label because some set in 20–40 minutes.
Above about one cubic yard, a mini-mix or ready-mix delivery tends to be cheaper and produces a better slab. The calculator flags this threshold so you can get a quote before buying a pallet of bags.
Reference table
| Use | Extra |
|---|---|
| Formed pad or step | 5–10% |
| Post holes | 10–20% |
| Repairs / patching | 15%+ |
Key facts
- 80 lb bags per cu yd
- 45
- 60 lb bags per cu yd
- 60
- 40 lb bags per cu yd
- 90
- Ready-mix worth pricing above
- ≈ 1 cu yd (0.76 m³)
Tips & common mistakes
- Buy one or two spare bags and return unopened ones — running short mid-pour leaves a cold joint.
- Bags left outside absorb moisture; lumpy bags should not be used for structural work.
- A wheelbarrow comfortably mixes two 80 lb bags at a time; a small mixer saves your back above ~20 bags.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45 bags, based on a typical yield of 0.6 cu ft per 80 lb bag (27 ÷ 0.6 = 45).
How many 60 lb bags are in a cubic yard?
About 60 bags at 0.45 cu ft per bag.
How much does a 20 kg bag of concrete cover?
Roughly 9–10 liters of placed concrete, so about 0.09 m² at 10 cm thick. Check the bag — yields vary by brand.
Should I buy 60 lb or 80 lb bags?
80 lb bags are usually cheaper per cubic foot; 60 lb bags are easier to lift and mix. The results show counts for both.
When should I switch to ready-mix?
Once you pass about 1 cubic yard (roughly 45 × 80 lb bags), ready-mix is often cheaper and gives a better, more consistent finish.
Sources
- Quikrete – bagged concrete product data — checked 2026-10; verify before launch
- Sakrete – concrete mix yields — checked 2026-10; verify before launch
- Tarmac (UK) – bagged concrete and postcrete — checked 2026-10; verify before launch
Default values (bag yields, coverage rates, densities) are typical figures from manufacturer literature. Always check the label on the product you buy.
Related calculators
- Concrete Slab CalculatorEstimate cubic yards, cubic meters and bags of concrete for a slab, patio or pad — with waste factor, the formula and a shopping list.
- Gravel CalculatorEstimate gravel, crushed stone or pea gravel in cubic yards, cubic meters, short tons and tonnes for paths, driveways and bases.
- Square Footage CalculatorFind the area of a room or yard in square feet, square meters and square yards — rectangles, triangles, circles and trapezoids.
Cite or embed this calculator
DIYCalcLab. “Concrete Bag Calculator.” Oct 18, 2026. https://diycalclab.com/concrete/bag-calculator/
An embeddable version for blogs and contractor sites is planned.
Estimates only. Verify quantities with your supplier and local building codes. For structural, electrical or safety-critical work, consult a licensed professional. Full disclaimer.