A little planning. The right amount of concrete. Calculate volume, bags, and cost.
A rectangular slab with an even thickness. Measure each area without overlapping.
Drag to rotate · Scroll or pinch to zoom. Focus the model and use arrow keys to rotate; Home resets.
Proportions follow your inputs. View one piece; quantity and reserve affect the estimate.
Allow for uneven ground, spillage, and small measurement differences.
Follow your inputs through the concrete calculator, one step at a time. Lengths are converted to meters before calculating volume. Figures below show up to 12 significant digits; ≈ means approximately equal. The calculation keeps full intermediate precision, so rounding these displayed figures can give a slightly different answer.
| Dimension | Your input | Converted to meters |
|---|---|---|
| L · Length | 10 ft | 10 × 0.3048 ≈ 3.048 m |
| W · Width | 10 ft | 10 × 0.3048 ≈ 3.048 m |
| T · Thickness | 4 in | 4 × 0.0254 ≈ 0.1016 m |
Quantity: 1
Formula for one piece: Length × width × thickness.
Vsingle = 3.048 × 3.048 × 0.1016 ≈ 0.9438948864 m³
Varea = Vsingle × quantity ≈ 0.9438948864 × 1 ≈ 0.9438948864 m³
A rectangular slab with an even thickness. Measure each area without overlapping.
Vnet = sum of area volumes ≈ 0.9438948864 ≈ 0.9438948864 m³
Vextra = Vnet × reserve / 100 ≈ 0.9438948864 × 10% ≈ 0.09438948864 m³
Vrequired = Vnet + Vextra ≈ 0.9438948864 + 0.09438948864 ≈ 1.03828437504 m³
Product: QUIKRETE No.1101 · 80 lb. Yield per bag: 0.6 ft³.
Y = 0.6 × 0.028316846592 ≈ 0.0169901079552 m³ per bag
Unrounded bags = Vrequired ÷ Y ≈ 1.03828437504 ÷ 0.0169901079552 ≈ 61.1111111111
Round up after combining all areas: 62 whole bags. At an exact integer boundary, insignificant floating-point noise is ignored.
Vbulk = Vrequired ÷ 0.764554857984 ≈ 1.35802469136 yd³
No supplier increment entered: order volume ≈ 1.35802469136 yd³.
Bag cost: no price entered.
Ready-mix cost: no price entered.
Bagged mix and ready-mix are alternatives, not quantities to add together. Supplier increments do not change the bag count. Costs exclude delivery, pumping, labor, tax and short-load charges.
Measurements, quantities & material costs
| Measurement | Value |
|---|---|
| Length | 10 ft |
| Width | 10 ft |
| Thickness | 4 in |
| Quantity | 1 |
Length × width × thickness × quantity → 1.234568 yd³
Choose bagged mix OR ready-mix. These options are alternatives, not additive.
The formulas are here to check. So are the assumptions that can change your order.
A concrete calculator turns measured dimensions into the volume of concrete needed for a project. Instead of estimating by eye, you choose a shape, enter its dimensions, and get quantities in cubic yards, cubic meters, and cubic feet. This concrete calculator also converts the required volume into whole bags and optional material costs.
Use the concrete calculator when planning a patio, shed base, rectangular footing, wall, circular pad, solid staircase, or ramp. The result describes material quantity for the dimensions you supply. The concrete calculator does not choose a safe structural thickness, reinforcement layout, or concrete strength for you.
The concrete calculator estimates finished concrete volume and bags of premixed concrete. Cement is one ingredient in concrete. It cannot infer separate quantities of cement, sand, aggregate, or water from your dimensions alone.
Start with the example, then replace every measurement with your own. The concrete calculator recalculates as you edit valid inputs. Check the shape and unit beside each field before using the result; a correctly entered number in the wrong unit can describe a very different project.
Vrequired = (V₁q₁ + V₂q₂ + …) × (1 + r / 100)
Vᵢ is one shape’s volume; qᵢ is its quantity; r is the reserve percentage. The concrete calculator combines areas before adding reserve.
Select Slab / footing for a rectangular slab, Wall for a solid rectangular wall, or another matching shape. Enter length, width, thickness, diameter, or height as shown. The concrete calculator accepts decimal dimensions and an integer quantity for identical pieces. Add separate areas when dimensions differ.
For an L-shaped patio, split the footprint into rectangles that do not overlap. The concrete calculator adds all areas, so entering intersecting rectangles would count their shared corner twice. Name each area to make the breakdown easy to review.
The concrete calculator starts with a visible 10% reserve. Choose 0%, 5%, 10%, or enter a custom percentage for your conditions. Net volume is the geometric amount; total required includes reserve. The concrete calculator adds this allowance once after combining areas, rather than repeatedly during each calculation.
Uneven ground and measurement uncertainty vary by project. Review the reserve with your supplier or installer. The concrete calculator displays the extra volume separately so you can see exactly how the setting changes your estimate.
The concrete calculator converts dimensions to a common length unit, applies the selected geometry formula, and multiplies by quantity. It sums the areas before calculating reserve, bags, and costs. Displayed numbers are rounded for readability, while the concrete calculator retains intermediate precision for subsequent calculations.
V(ft³) = L(ft) × W(ft) × T(in) / 12 V(yd³) = L(ft) × W(ft) × T(in) / 324
For a uniform rectangular slab: L = length, W = width, T = thickness. These concrete calculator formulas give net volume before quantity and reserve.
V(m³) = L(m) × W(m) × T(mm) / 1,000 1 yd³ = 27 ft³ = 0.764554857984 m³
Convert thickness to meters first. The concrete calculator keeps conversion precision until the final display. Exact conversions: 1 ft = 0.3048 m; 1 in = 0.0254 m; 1 ft³ = 0.028316846592 m³; 1 m³ = 1,000 L.
For a rectangular slab, volume equals length × width × thickness. When length and width are in feet and thickness is in inches, divide their product by 12 for cubic feet or by 324 for cubic yards. The concrete calculator performs these conversions without truncating four inches to 0.33 feet.
A yard of concrete usually refers to a cubic yard when ordering volume. One cubic yard equals 27 cubic feet. This concrete calculator labels volume with yd³ or ft³ to distinguish it from a length or surface area.
For a metric concrete calculator example, enter a length of 3 m, a width of 2 m, and a thickness of 100 mm. The net result is 0.6 m³. The concrete calculator supports m, cm, mm, ft, and in independently, so mixed measurement units do not require manual conversion.
Changing a unit in the concrete calculator converts the existing value instead of reinterpreting it. Check the converted fields before continuing. Enter feet as a decimal or choose inches; this version does not provide separate feet-plus-inches boxes.
Project names describe the job, while geometry determines the calculation. The same concrete calculator can estimate several applications when their shapes match. Select the actual geometry and supply the required dimensions instead of assuming a patio, driveway, or footing always has a standard thickness. Drag the concrete calculator’s 3D preview to inspect one piece, zoom in, or rotate to inspect the top and bottom. Red dimension marks identify selected edges; rotate back to view marks hidden behind the model. Its proportions follow valid dimensions; quantity and reserve affect the numerical estimate. A reference diagram remains available if 3D is unsupported.
Each concrete calculator shape formula gives V for one piece. Use the same length unit throughout: meters produce m³; feet produce ft³. Multiply by quantity, then add reserve.
V = L × W × T
L = length; W = width; T = uniform thickness.
V = L × H × T
H = wall height. Use solid sections without openings.
V = π × D² × H / 4
D = full diameter; H = height or circular slab thickness.
V = π × (D² − d²) × H / 4
D = outer diameter; d = inner diameter; 0 ≤ d < D.
V = W × R × H × n(n + 1) / 2
R = tread depth; H = rise per step; n = step count. Solid fill; top tread included, separate landing excluded.
V = L × W × (T₁ + T₂) / 2
L = horizontal length; T₁ and T₂ = vertical end thicknesses. Thickness changes linearly.
Use the rectangular mode as a concrete calculator for a patio slab, driveway section, garage floor, or shed base with uniform thickness. For a slab with different depths, create separate areas. The concrete calculator does not include a gravel base, reinforcement, excavation, or thickened edges automatically.
Use the concrete calculator to multiply a rectangular footing’s length, width, and depth. For a wall, enter length, height, and thickness. Divide walls around door or window openings into solid rectangles. The concrete calculator estimates their material volume; it does not assess bearing capacity or retaining-wall stability.
For a solid round column, the concrete calculator uses π × diameter² × height ÷ 4. For a hollow cylinder, it subtracts the inner circular area before multiplying by height. The concrete calculator requires the inner diameter to be smaller than the outer diameter; enter full diameters rather than radii.
The concrete calculator supports solid steps filled down to the ground: width × tread depth × rise × n(n + 1) ÷ 2. The top tread is already included. Add a separate landing as another area. For a linear ramp, the concrete calculator multiplies horizontal length and width by the average end thickness.
Do not use the solid-stair concrete calculator result for suspended stairs or a thin concrete layer over fill. Those structures need a different geometric model. Ramp thicknesses are measured vertically; one end may be zero, but both cannot be zero.
A concrete bag calculator needs the volume produced by each bag, not just its weight. This concrete calculator uses documented QUIKRETE Concrete Mix No.1101 yields for its presets. Select the product and bag size, or enter a custom yield taken from your own product’s packaging or data sheet.
Bags = ⌈Vrequired / Y⌉
Y = volume yielded per bag, in the same unit as Vrequired. ⌈ ⌉ means round up to a whole number. The concrete calculator rounds after combining areas.
For No.1101, an 80 lb bag yields approximately 0.60 ft³ and a 60 lb bag approximately 0.45 ft³. With no reserve, the concrete calculator therefore gives 45 bags of 80 lb or 60 bags of 60 lb for one cubic yard. These are alternative purchase quantities, not bags to add together.
The concrete calculator divides combined required volume by yield and rounds up once. A requirement of 0.61 ft³ with a 0.60 ft³ yield needs two bags. Two separate areas totaling 0.60 ft³ need one bag if purchased together without reserve.
The concrete calculator also offers 40, 50, and 90 lb No.1101 presets, with approximate yields of 0.30, 0.375, and 0.675 ft³ respectively. For another mix, select Custom product / yield and enter output in ft³, yd³, m³, or liters. The concrete calculator does not assume that every 80 lb product, or every 20 kg or 25 kg bag, produces the same volume.
Open Estimate material cost to add your own supplier prices. The concrete calculator leaves prices blank initially, so it never presents an invented local quote. Compare bagged mix and ready-mix as separate purchasing options using current prices for the products and units you intend to buy.
Cbags = Bags × Pbag Vorder = ⌈Vrequired / s⌉ × s Cbulk = Vorder × Pvolume
P = your supplier’s unit price; s = a positive order increment. Without s, Vorder = Vrequired. Match volume units. The concrete calculator treats bagged mix and ready-mix as alternatives.
For bags, the concrete calculator multiplies the rounded bag count by price per bag. Each bag option keeps its own entered price. For ready-mix, the concrete calculator multiplies the order volume by price per selected volume unit. Currency selection labels your quote; it does not convert prices using exchange rates.
Delivery, labor, pumping, short-load charges, and tax are excluded. The concrete calculator produces a material estimate, not an installed concrete slab cost or a binding supplier quote. Compare complete quotes separately before choosing an order.
If a supplier sells in quarter-yard increments, enter 0.25 with yd³ selected. The concrete calculator rounds 1.358024… yd³ of required concrete to a 1.5 yd³ bulk order. Leave the increment blank for exact volume. The concrete calculator keeps bag quantities based on the original requirement, independent of bulk ordering rules.
Use these worked examples to understand the result, then replace the dimensions with your own. The concrete calculator initially loads the first slab as an example. None of these dimensions is a recommendation for structural design, and the example bag price is not a market quotation.
Net volume is 10 × 10 × 4 ÷ 12 = 33.333333… ft³, or 1.234567… yd³. With 10% reserve, the concrete calculator returns 36.666666… ft³, or about 1.358 yd³. Dividing by 0.60 ft³ per 80 lb No.1101 bag gives 61.111111… bags, rounded up to 62.
Enter an example price of 7 per bag and the concrete calculator returns 434 in the selected currency. Alternatively, with no reserve, no order increment, and 150 per yd³, the concrete calculator returns 185.19. It uses unrounded volume rather than multiplying the displayed 1.235 figure.
The concrete calculator first converts 100 mm to 0.1 m, giving 3 × 2 × 0.1 = 0.6 m³ net. A 10% reserve produces 0.66 m³. With a custom yield of 0.01 m³ per bag, the concrete calculator gives 66 bags; changing the reserve to 5% gives 0.63 m³ and 63 bags.
Enter length, width, and thickness in the concrete calculator, then choose your reserve. Surface area alone is insufficient because depth changes the volume. For a uniformly thick rectangle, the concrete calculator multiplies all three dimensions after converting their units.
Yes. Select Round / column in the concrete calculator and enter the full diameter plus slab thickness in the height field. Use quantity for identical circular pads. A hollow circular section requires Hollow cylinder mode and both inner and outer diameters.
Yes, the concrete calculator initially adds 10%, shown beside the total and separately in the breakdown. You can change it or select 0%. Confirm the allowance for your site rather than treating the starting setting as a universal requirement.
Round / column calculates a full cylinder. The concrete calculator does not automatically subtract a post occupying that space, and it has no dedicated post-hole subtraction mode. Do not treat a full-cylinder concrete calculator result as the exact net quantity around an embedded post.
No. The concrete calculator estimates geometry and purchasing quantities. Follow the selected mix manufacturer’s instructions for water and preparation. Concrete strength, reinforcement, and structural suitability depend on information beyond the dimensions and are not calculated by this concrete calculator.
Compare dimensions, units, reserve, product yield, and rounding rules. A concrete calculator using a different bag product or silently adding waste can give a different answer. For stairs, confirm whether the top tread or a separate landing is included before comparing volumes.
Check the calculation details beside your project and review the calculation guide for the full formula reference. Geometry and worked examples on this page match the implemented modes.
Maintained by Evan Brooks. Content and functionality checked . Confirm current product specifications before ordering.
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