CONCRETE BAG CALCULATOR

Concrete Bag Calculator — How Many Bags Do I Need?

Already know your concrete volume? Enter it in cubic yards, cubic feet or cubic metres and see how many pre-mixed bags you need. Compares all common bag sizes — 40, 50, 60 and 80 lb — so you can choose the most practical option for your project.

Concrete volume needed

Bag size

Waste allowance

Bags needed
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Enter volume to calculate bag count.

Find Out How Many Bags of Concrete You Need

Already know how much concrete your project needs? The Interior Tailor Concrete Bag Calculator converts that volume into a bag count in seconds. Enter your volume in cubic yards, cubic feet or cubic metres, choose a 40, 50, 60 or 80 lb bag, add a waste allowance, and see how many pre-mix bags to buy. It is the quickest way to compare bag sizes, price a small pour and decide whether bags or ready-mix concrete makes more sense.

What This Bag Calculator Does

  • Start from any volume: cubic yards, cubic feet or cubic metres.
  • Compare all common bag sizes: 40, 50, 60 and 80 lb bags, each with its approximate yield.
  • Waste allowance: add a percentage so you do not run short mid-pour.
  • Clear bag count: a single result to take straight to the store.
  • Pairs with the slab and concrete calculators: calculate volume first, then convert it to bags here.

Concrete Bag Yields at a Glance

  • 40 lb bag: ~0.30 ft³ (~8.5 L) — ideal for small repairs and posts
  • 50 lb bag: ~0.375 ft³ (~10.6 L)
  • 60 lb bag: ~0.45 ft³ (~12.7 L) — popular for medium jobs
  • 80 lb bag: ~0.60 ft³ (~17 L) — most economical, fewest bags to mix

Yields are approximate and vary slightly by brand. Always check the stated yield on the specific bag you purchase. One cubic yard requires approximately 45 bags of 80 lb pre-mix or 60 bags of 60 lb.

When to Use Bags vs Ready-Mix Concrete

The break-even point is roughly 1 cubic yard (27 cubic feet). Below that, bags are convenient and flexible; above that, ready-mix is more economical and practical.

  • Use bags for: fence posts, small slabs under 40 sq ft, repairs, footings
  • Use ready-mix for: driveways, full-room slabs, foundations, pours over 1 yd³
  • Mixing 45+ bags by hand takes 4–6 hours and results in inconsistent water ratios
  • Ready-mix minimum load is usually 1 yard — some suppliers offer ½-yard "short loads" at a premium

Tips for Mixing Concrete from Bags

  • Use a mechanical mixer for jobs over 10 bags — hand mixing is exhausting and inconsistent
  • Add water gradually — too much water is the most common mistake and weakens concrete significantly
  • Typical water: approximately 3 quarts (2.8 L) per 80 lb bag
  • Mix until uniform with no dry pockets — about 3–5 minutes per batch in a mixer
  • Do not mix more than you can place and finish in 30–45 minutes
  • Work in shaded conditions in hot weather to extend working time

When Bagged Concrete Makes Sense

Pre-mix bags are best for small, manageable jobs:

  • Fence, mailbox and deck posts
  • Small slabs and pads
  • Repairs and patching
  • Small footings
  • Locations a truck cannot reach

Bag Counts at a Glance

Here is how one volume turns into different bag counts. The first table starts from half a cubic yard with a 10% waste allowance. The second shows approximate bags per full cubic yard before waste.

Half a cubic yard (13.5 cu ft) plus 10% waste = 14.85 cu ft

Bag Counts at a Glance
Bag sizeApprox. yieldBags needed
40 lb0.30 cu ft50 bags
50 lb0.375 cu ft40 bags
60 lb0.45 cu ft33 bags
80 lb0.60 cu ft25 bags

Approximate bags per cubic yard (27 cu ft), before waste

Bag Counts at a Glance
Bag sizeBags per cubic yard
40 lbAbout 90
50 lbAbout 72
60 lbAbout 60
80 lbAbout 45

Yields vary slightly by brand, so check the stated yield on the bag you buy. Round up to a whole bag.

Tips for Buying and Mixing Bagged Concrete

  • Choose 80 lb bags for fewer bags to mix, or 60 lb bags if lighter lifting matters more.
  • For anything above about 10 bags, use a mechanical mixer rather than mixing by hand.
  • Add water gradually and follow the label. Too much water weakens the finished concrete.
  • Only mix what you can place and finish in about 30 to 45 minutes.
  • Above roughly one cubic yard, compare the cost and labour with a ready-mix delivery.

Frequently Asked Questions

How many bags of concrete do I need for a 4×4 fence post?

A standard post hole (12 in diameter, 36 in deep) holds approximately 2.35 cu ft. That requires four 80 lb bags or five 60 lb bags. Most installers use two 80 lb bags per post as a quick estimate.

What is the difference between concrete mix and mortar mix?

Concrete mix contains Portland cement, sand and coarse aggregate (gravel). Mortar mix contains cement and sand only — no gravel. Concrete is used for structural pours; mortar is used for setting blocks, bricks and tiles.

Can I add too little water to concrete?

Yes. Too little water prevents complete hydration of the cement particles, resulting in crumbly, weak concrete. Follow the bag's water recommendation. Adding extra water to improve workability reduces strength — use a plasticizer additive instead if needed.

How many 80 lb bags of concrete make one cubic yard?

About 45 bags, based on a yield of roughly 0.6 cubic feet per bag. A cubic yard is 27 cubic feet, so 27 divided by 0.6 gives 45.

Which bag size is the best value?

The 80 lb bag is usually the most economical and needs the fewest bags. Smaller 40 to 60 lb bags are easier to lift and suit small repairs and posts. Compare the price per cubic foot of yield, not the price per bag.

How does the calculator work out my bag count?

It adds your waste allowance to the volume, then divides by the approximate yield of the bag size you choose. Always round up to a whole bag.