Ratios are by volume, not by weight. Strengths are nominal.
Pour 1
Work backwards — see what a batch this size makes.
Advanced options
One 94 lb sack is one cubic foot.
By weight. Lower means stronger and harder to work.
Dry ingredients shrink when mixed. 1.54 is standard.
This concrete mix calculator works out how much cement, sand, gravel and water you need for any mix ratio — as bags, cubic feet, pounds and gallons. It also gives you the one-bag batch recipe, which is what you actually work from at the mixer.
The short answer
The standard general-purpose mix is 1 part cement, 2 parts sand, 3 parts gravel by volume, giving roughly 3,000 PSI. One 94 lb sack of Portland cement plus 2 ft³ sand + 3 ft³ gravel + 5.6 gallons water makes about 3.9 cubic feet of concrete.
A full cubic yard at 1:2:3 takes about 7 bags of cement, 14 ft³ of sand and 21 ft³ of gravel.
On this page
How to use this concrete mix calculator
Pick your mix ratio at the top, then tell the calculator how much concrete you need. Four modes:
- Slab — enter length, width and thickness
- Post holes — diameter, depth and how many
- Known volume — you already have cubic yards, feet or metres
- One-bag batch — work backwards from a number of cement bags to see what they make
That last mode is worth knowing about. On site you don’t measure out 14 cubic feet of sand — you mix one bag at a time and repeat. Setting the calculator to one bag tells you the exact recipe for a single batch and how much concrete it produces, so you know how many rounds you’re in for.
Under Advanced options you can change cement bag size, water-cement ratio and the dry-volume factor. That last one is why different websites give different answers, covered below.
Concrete mix ratios by strength
Ratios are quoted as cement : sand : gravel, measured by volume, not by weight. More cement means more strength and more cost.
| Ratio | Approx. PSI | 94 lb bags/yd³ | Typical use |
|---|---|---|---|
| 1 : 1 : 2 | 5,000 | 10.4 | Columns, beams, high-strength structural work |
| 1 : 1.5 : 3 | 4,000 | 7.6 | Driveways, garage slabs, heavy vehicle loads |
| 1 : 2 : 3 | 3,000 | 6.9 | General purpose — patios, paths, shed floors, posts |
| 1 : 2 : 4 | 2,500 | 5.9 | Footings, non-structural fill, garden walls |
| 1 : 3 : 6 | 2,000 | 4.2 | Mass concrete, blinding layers, backfill |
A ratio is a rule of thumb, not a mix design. Actual strength depends on aggregate quality and grading, water content, compaction, curing and temperature. A 1:2:3 mix carelessly batched with wet sand and a generous hose can easily test below 2,500 PSI. For structural work — anything an inspector will look at — follow the specification from your engineer or a proper mix design to ACI 211.1, not a ratio from a website.
The formula behind the calculator
Three steps, and only the middle one is unobvious.
1. Dry volume = Wet volume × 1.54
2. Each material = Dry volume × (its parts ÷ total parts)
3. Cement bags = Cement volume ÷ 1 ft³ per 94 lb sack
The 1.54 is the dry-volume factor — dry ingredients occupy about 54% more space
than the concrete they produce, because sand fills the voids between gravel
and cement paste fills the voids between sand.
Worked example — 1 cubic yard at 1:2:3
Why published bag counts disagree
Search for how many bags of cement make a cubic yard of 1:2:3 concrete and you’ll find 5.5, 6, 6.9 and 7.5 all stated confidently. That’s a real spread, and it’s worth understanding rather than guessing which to trust.
The most widely repeated figure is “5.5 bags of cement, 17 ft³ of sand and 18 ft³ of gravel per cubic yard”. Work the ratio backwards and it comes out at roughly 1 : 3.1 : 3.3 — which is a perfectly reasonable mix, but it is not 1:2:3. It’s leaner in cement and richer in sand. The figure is correct; the label attached to it isn’t.
Check the total: 5.5 + 17 + 18 = 40.5 ft³ of dry material per 27 ft³ of concrete. That’s a dry-volume factor of 1.50, essentially identical to the 1.54 used here. The sources agree on the method entirely. They disagree about which ratio the numbers describe, and one of them has mislabelled it.
The second cause of variation is the dry-volume factor itself. Most sources use 1.54; some use a yield factor of 0.65 or 0.67 expressed the other way round, which is the same thing. A handful use 1.50 or 1.57 depending on assumed aggregate grading. The spread that produces is only a few percent — nothing like the gap above.
This calculator shows the dry-volume factor it uses and lets you change it, so you can reconcile its output against any other source rather than wondering which is right.
The one-bag batch
Nobody measures out 14 cubic feet of sand. You mix one bag of cement at a time and repeat until the pour is full, so the number that matters on site is the single-batch recipe.
| Ratio | Sand | Gravel | Water | Makes |
|---|---|---|---|---|
| 1 : 1 : 2 | 1 ft³ (100 lb) | 2 ft³ (200 lb) | 5.6 gal | 2.6 ft³ |
| 1 : 1.5 : 3 | 1.5 ft³ (150 lb) | 3 ft³ (300 lb) | 5.6 gal | 3.6 ft³ |
| 1 : 2 : 3 | 2 ft³ (200 lb) | 3 ft³ (300 lb) | 5.6 gal | 3.9 ft³ |
| 1 : 2 : 4 | 2 ft³ (200 lb) | 4 ft³ (400 lb) | 5.6 gal | 4.5 ft³ |
| 1 : 3 : 6 | 3 ft³ (300 lb) | 6 ft³ (600 lb) | 5.6 gal | 6.5 ft³ |
All figures are per one 94 lb sack of cement at a 0.50 water-cement ratio. Note the water stays the same across every row — it’s tied to the cement, not to the total volume.
Shovel loads vary by 30% or more between people, and by more than that between a dry pile and a damp one. Use a bucket or a marked box as your measure and fill it the same way every time. A five-gallon bucket is 0.67 ft³, so a 1:2:3 batch is one bag of cement, three buckets of sand and four and a half of gravel — close enough for hand mixing, and far more consistent than counting shovels.
The water-cement ratio
This single number has more effect on final strength than the aggregate ratio does, and it’s the one people get wrong most often.
Water-cement ratio is the weight of water divided by the weight of cement. A 94 lb sack at w/c 0.50 takes 47 lb of water, which is 5.6 US gallons.
| w/c | Water per 94 lb bag | Effect on strength | Workability |
|---|---|---|---|
| 0.40 | 4.5 gal | Highest | Stiff, needs vibration |
| 0.45 | 5.1 gal | High | Firm, hard work by hand |
| 0.50 | 5.6 gal | Standard | Workable — the usual choice |
| 0.55 | 6.2 gal | Reduced | Easy to place |
| 0.60 | 6.8 gal | Noticeably lower | Wet, prone to segregation |
Sand from an outdoor pile commonly holds 3–6% moisture by weight. On a one-bag 1:2:3 batch that’s 200 lb of sand carrying 6–12 lb of hidden water — a quarter to half of the water you were about to add, already in the mix.
This is why the mix looks wet before you’ve added much from the hose, and why adding water to reach the “right” total is how batches end up over-wet. Start with about two thirds of the calculated water, mix, then add the rest gradually only if you need it.
Quantities per cubic yard
| Ratio | Cement | Sand | Gravel | Water |
|---|---|---|---|---|
| 1 : 1 : 2 | 10.4 bags | 10.4 ft³ | 20.8 ft³ | 59 gal |
| 1 : 1.5 : 3 | 7.6 bags | 11.3 ft³ | 22.7 ft³ | 43 gal |
| 1 : 2 : 3 | 6.9 bags | 13.9 ft³ | 20.8 ft³ | 39 gal |
| 1 : 2 : 4 | 5.9 bags | 11.9 ft³ | 23.8 ft³ | 33 gal |
| 1 : 3 : 6 | 4.2 bags | 12.5 ft³ | 24.9 ft³ | 24 gal |
Bags are 94 lb Portland cement at 1 ft³ each, water at w/c 0.50, no waste allowance included. In 50 kg bags, a cubic yard at 1:2:3 takes about 5.9 bags instead of 6.9, because a 50 kg sack holds more than a 94 lb one.
Choosing your materials
| Material | What to buy | What to avoid |
|---|---|---|
| Cement | Type I or Type I/II Portland cement. Bags should be soft and free-flowing. | Hard lumps that won’t crush by hand — the cement has partly hydrated and won’t reach strength. |
| Sand | Concrete sand or sharp sand — coarse, angular, well graded. | Play sand and beach sand. Too fine, too uniform, and beach sand carries salt that corrodes reinforcement. |
| Gravel | Washed crushed stone, ¾ in nominal for most slabs. Angular faces interlock. | Dirty or dusty aggregate — clay coating stops cement bonding to the stone. |
| Water | Clean enough to drink is the standard test. | Seawater, and anything with visible organic matter or oil. |
Aggregate size matters for thin sections. Use ⅜ in stone rather than ¾ in where the pour is under about 3 inches thick or where reinforcement is tightly spaced — larger stone bridges across gaps and leaves voids beneath.
Is mixing your own actually worth it?
Under 0.25 yd³
Use premix bags
Buying three separate materials for a few cubic feet means three trips or three deliveries. Premix costs more per yard but you just add water.
0.25 – 2 yd³
Mixing your own wins
Roughly $120–$150 per yard in materials against $250–$400 for the same volume in premix bags. This is the range where the saving is real.
Over 2 yd³
Order ready-mix
Fourteen or more separate batches, each one slightly different, with the first setting before the last is placed. Delivered concrete is one consistent load.
Materials for one cubic yard at 1:2:3 come to roughly $125–$155 in 2026 — about 7 bags of cement at $16–$20, plus about 1.7 tons of sand and gravel at $35–$45 per ton. Ready-mix delivered runs $125–$175 per yard before short-load fees, so the saving is thin at volume and disappears entirely once you value your time.
How to mix
- Measure everything by volume with the same container, filled the same way each time.
- Combine the dry materials first — cement, sand and gravel — and mix until the colour is uniform with no streaks of grey or pale sand.
- Add about two thirds of the water and mix.
- Add the rest gradually, stopping as soon as the mix holds its shape when you cut a groove through it with a trowel.
- Mix for at least three minutes after the last water goes in. Under-mixing leaves dry pockets that never gain strength.
- Place within 30–45 minutes, sooner in hot weather.
- Keep it damp for seven days after placing. Curing affects final strength more than most people expect.
Mix ratio mistakes to avoid
- Adding water to make it easier to place. Every extra gallon per bag costs real strength, permanently.
- Ignoring moisture in the sand. Damp sand can supply a third of your water before you touch the hose.
- Measuring by shovel. Shovel loads vary by 30%, which is more variation than the difference between two mix ratios.
- Using play sand or beach sand. Too fine to develop strength, and beach sand carries corrosive salt.
- Forgetting the dry-volume factor. Dry ingredients take about 54% more space than the concrete they make.
- Trusting a bag count without checking the ratio it assumes. Widely quoted figures describe different mixes.
- Treating a nominal ratio as a mix design. Structural work needs a specification, not a rule of thumb.
Frequently asked questions
What is the correct ratio for mixing concrete?
1 part cement, 2 parts sand and 3 parts gravel by volume is the standard general-purpose mix, giving roughly 3,000 PSI. Use 1:1.5:3 for driveways and garage slabs at around 4,000 PSI, and 1:2:4 for footings and non-structural work at around 2,500 PSI.
How many bags of cement do I need for 1 cubic yard?
About 7 bags of 94 lb Portland cement for a 1:2:3 mix, along with 13.9 ft³ of sand and 20.8 ft³ of gravel. A leaner 1:2:4 mix takes 5.9 bags, and a stronger 1:1.5:3 takes 7.6. In 50 kg bags a 1:2:3 yard takes about 5.9.
How much concrete does one bag of cement make?
About 3.9 cubic feet at a 1:2:3 mix — one 94 lb sack plus 2 ft³ of sand, 3 ft³ of gravel and 5.6 gallons of water. At 1:2:4 the same bag makes 4.5 ft³, and at 1:1:2 it makes only 2.6 ft³ because the mix is much richer in cement.
Why do different websites give different bag counts?
Almost always because the ratio has been mislabelled. The widely quoted “5.5 bags, 17 ft³ sand, 18 ft³ gravel per yard” works out to a 1:3.1:3.3 mix, not 1:2:3 — the figures are fine but the label is wrong. A smaller second cause is the dry-volume factor used, typically 1.50 to 1.57, which only accounts for a few percent difference.
What is the dry-volume factor?
Dry cement, sand and gravel occupy about 54% more space than the concrete they produce, because sand fills the voids between gravel particles and cement paste fills the voids between sand grains. Multiplying wet volume by 1.54 gives the dry material you need to buy. Some sources express it as a yield factor of 0.65 instead, which is the same thing.
How much water per bag of cement?
About 5.6 US gallons per 94 lb bag at a water-cement ratio of 0.50. That drops to 5.1 gallons at 0.45 and 4.5 at 0.40 for stronger mixes. Remember that damp sand already carries water — start with two thirds and add the rest only if needed.
What is the strongest concrete mix ratio?
Among common nominal mixes, 1:1:2 gives roughly 5,000 PSI. But strength depends more on the water-cement ratio than the aggregate ratio — a 1:1:2 mix batched too wet can easily test lower than a well-controlled 1:2:3. For anything genuinely high strength, use a designed mix rather than a nominal ratio.
Can I use builder’s sand or play sand for concrete?
No. Concrete needs sharp, coarse, well-graded concrete sand. Play sand is too fine and too uniform to develop strength, and beach sand carries salt that corrodes any reinforcement. Ask a supplier for concrete sand or sharp sand specifically.
Is mixing your own concrete cheaper than bags?
Yes, at the right volume. Raw materials run roughly $125–$155 per cubic yard against $250–$400 for the same volume in premix bags. But below about a quarter of a yard the logistics aren’t worth it, and above two yards ready-mix delivered wins on both cost and consistency.
How do I measure a mix ratio accurately?
Use a bucket or marked box, not a shovel — shovel loads vary by 30% or more. A five-gallon bucket holds 0.67 ft³, so a one-bag 1:2:3 batch is roughly three buckets of sand and four and a half of gravel. Fill the container the same way every time.
What size gravel should I use?
Washed crushed stone at ¾ inch nominal for most slabs and footings. Drop to ⅜ inch for sections under about 3 inches thick or where reinforcement is tightly spaced, since larger stone bridges across gaps and leaves voids underneath.
Can I use this concrete mix calculator in metric?
Yes. Switch the header toggle to m / mm for dimensions, and choose 50 kg, 40 kg or 25 kg cement bags under Advanced options. Results show cubic feet, cubic yards and cubic metres together.
Standards and method
- ACI 211.1 — Standard practice for selecting proportions for normal, heavyweight and mass concrete
- ACI 318 — Building code requirements for structural concrete
- ASTM C150 — Portland cement · ASTM C33 — Concrete aggregates
- Portland cement density taken as 94 lb/ft³, giving one cubic foot per 94 lb sack — the US standard sack convention
- Loose dry sand and gravel taken as 100 lb/ft³; actual density varies with grading and moisture
- Dry-volume factor of 1.54 applied, adjustable in the calculator
Related calculators
Concrete Bag CalculatorPremix bags if you’d rather not batch
Concrete Slab CalculatorCubic yards with rebar and mesh
Post Hole CalculatorDepth, diameter and concrete per post
Gravel CalculatorAggregate by the ton or yard
Slab Cost CalculatorCompare mixing your own against hiring out
How this concrete mix calculator works out its numbers
Wet volume is calculated from your dimensions, multiplied by the dry-volume factor to give the total dry material required, then divided between cement, sand and gravel in proportion to the mix ratio. Cement volume is converted to bags using a Portland cement density of 94 lb/ft³, so one 94 lb sack is exactly one cubic foot — the standard US sack convention. Sand and gravel are converted to weight at 100 lb/ft³ loose and dry. Water is calculated from cement weight at the selected water-cement ratio, using 8.34 lb per US gallon.
The dry-volume factor defaults to 1.54 and is adjustable, because it is the main assumption that varies between published sources. Changing it lets you reconcile this calculator’s output against any other reference.
Nominal mix ratios are rules of thumb, not mix designs. The PSI values shown are indicative of what a well-batched, well-cured mix achieves in good conditions, and are not a specification. Aggregate quality and grading, moisture content, compaction, curing and temperature all move actual strength significantly. For structural concrete, follow a designed mix to ACI 211.1 and the specification from your engineer or local code — not a ratio from a website.