How we calculate

Concrete

Open the Concrete calculator. Dimensions are converted to meters before calculating. Repeated areas are multiplied by their count, then combined.

• Slabs and rectangular footings: volume = length × width × depth.
• Solid round columns: volume = π × (diameter ÷ 2)² × height.
• Post holes: volume = (round hole area − post area) × depth. Round posts use π × (post diameter ÷ 2)²; square posts use side². The post is subtracted through the full depth.
• Solid steps: volume = width × tread × rise × n × (n + 1) ÷ 2, where n is the number of equal steps. No landing or hollow core is included.

Supply volume = combined net volume × (1 + waste percentage ÷ 100). The default 10% allowance is an editable starting point for measurement variation, uneven ground and handling losses. It is our planning default, not a required industry rate.

The QUIKRETE Concrete Mix No. 1101 data sheet gives approximate mixed yields of 0.60 ft³ per 80 lb bag, 0.45 ft³ per 60 lb bag and 0.375 ft³ per 50 lb bag. These are product-specific figures, not yields for every bag of that weight. Custom products require their own mixed yield.

Whole bags = supply volume ÷ yield per bag, rounded up. Ready-mix quantities remain in the selected volume unit; confirm order minimums and increments with your supplier. Prices are your entries, and results are material subtotals only.

Units and conversions

One cubic yard equals 27 ft³. One foot is exactly 0.3048 m, so 1 ft³ = 0.028316846592 m³. One yard is exactly 0.9144 m, so 1 yd³ = 0.764554857984 m³. One liter is 0.001 m³. These follow the NIST SI conversion definitions. The tools support US and metric dimensions; mixed units are converted before arithmetic.

Avoid overlapping areas. Quantity calculations do not select safe depths, reinforcement or structural designs.

Concrete Bags

Open the Concrete Bags calculator. Dimensions mode uses the same solid shapes and formulas as Concrete, with an editable 10% default allowance. Known-volume mode accepts ft³, yd³, m³ or liters.

For a net volume, supply = net × (1 + waste percentage ÷ 100). If the entered volume already includes waste, no additional allowance is added. Bags = supply volume ÷ mixed yield per bag, rounded up after combining the areas.

The US products use the QUIKRETE 1101 data sheet: 40 lb → 0.30 ft³, 50 lb → 0.375 ft³, 60 lb → 0.45 ft³ and 80 lb → 0.60 ft³. The Blue Circle Multi-Purpose Concrete technical sheet states a typical yield of around 0.01 m³ per 20 kg bag. All are approximate mixed yields. A custom product needs its own yield; mass alone does not tell us the volume.

This tool estimates complete bagged concrete, not separate cement, sand and aggregate recipes.

Gravel

Open the Gravel calculator. A rectangular bed uses length × width × depth. A circular bed uses π × (diameter ÷ 2)² × depth. Repeats and separate areas are combined without deducting overlaps automatically.

Loose supply volume = net bed volume × loose-per-compacted multiplier × (1 + waste percentage ÷ 100). If your measurements already describe loose placed material, the multiplier is 1. The default compacted-bed multiplier of 1.2 and 10% extra waste are separate, editable planning assumptions. Confirm both with your supplier; neither is a universal gravel requirement.

Supply mass = loose supply volume × loose bulk density. The indicative loose density presets are 1,500 kg/m³ for round river gravel and 1,700 kg/m³ for road gravel, from the Landscape Development Industry bulk-density reference. The default is 1,700 kg/m³. Grading, moisture and material affect density; use your supplier's value for the actual loose product. The reference does not establish our 1.2 default multiplier for every bed.

Mass-sized bags use supply mass ÷ bag mass; volume-sized bags use supply volume ÷ bag volume. Bags always round up. The default 25 kg bag is an editable example, not a named product yield. Bulk orders round up to your entered increment; an increment of 0 leaves the demand unrounded.

One metric tonne is 1,000 kg; one US short ton is 2,000 lb, or 907.18474 kg. A pound is exactly 0.45359237 kg under the NIST conversion definitions linked above. Weight and volume are not interchangeable without density.

Block & Mortar

Open the Block & Mortar calculator. Net wall area = (length × height − non-overlapping opening areas) × repeat count. Installed block equivalents = combined net wall area ÷ coordinating block face area. You may instead enter an installed block count.

As explained by Angelus Block's dimensions guide, nominal dimensions include the mortar joint. For specified block dimensions, the calculator adds your joint to length and height before dividing the wall area. Do not add a joint again to nominal dimensions. The default reference is nominal 8 × 8 × 16 in with a 3/8 in joint and face-shell bedding.

Block demand = installed equivalents × (1 + block allowance ÷ 100). The editable default is 5% for cuts and breakage. The block purchase rounds upward to your pack size; the default pack size is 1. The separate 10% mortar allowance is an editable starting point for handling losses. These defaults are planning choices, not prescribed waste rates.

Mortar products and recipes

The initial estimate has no mortar product selected, so it is incomplete until you choose one. Mortar is calculated from installed block equivalents, not extra purchased blocks.

• Reference complete premix: the QUIKRETE Mortar Mix 1102 data sheet says an 80 lb bag lays up to 13 standard 8 × 8 × 16 in blocks. Bags = installed equivalents × (1 + mortar allowance ÷ 100) ÷ 13, rounded up. This is approximate upper coverage, not guaranteed site coverage. A complete sanded premix does not require a separate sand purchase.
• Named site-mix alternative: the QUIKRETE Type S Masonry Cement 1125-71 sheet describes one 70 lb binder bag with 240 lb masonry sand, yielding about 2.75 ft³ of mortar or covering about 46 standard blocks. Batch demand uses that coverage, or the stated wet yield when a known wet volume is entered. Ingredient demand is calculated from unrounded batches, then rounded to each selected purchase package or increment. Spare purchased binder does not increase calculated sand demand.

Reference block coverage applies only to matching dimensions, joint and bedding assumptions. Other blocks or products require matching supplier coverage or a known wet volume with a matching yield. If an entered wet volume already includes allowance, we do not add it again.

Custom site mixes need a supplied loose-volume ratio, gauge size and matching batch yield or coverage. Mass-to-volume conversions need your matching density or mass-per-gauge calibration. There is no assumed generic dry-volume factor or sand density. The custom cement-and-sand model does not include lime; use a complete specified recipe where lime is required.

Only compatible materials and purchase assumptions combine in My project before final purchase rounding. Different products, currencies and recipes stay separate. This is for straight, rectangular, single-leaf mortared walls. It excludes grout, reinforcement, foundations, lintels, retaining-wall systems and an exact cutting schedule. It does not establish structural suitability.

How we test

We use fixed test inputs with expected answers worked out independently by hand. Automated tests check geometry, unit equivalence, product yields, allowances, package boundaries and compatible purchase aggregation. Browser tests exercise typing, corrections, saving, sharing and other supported interactions.

We also compare selected cases with other public calculators. Different allowances and product assumptions can produce different answers. A comparison is a useful check, not proof that a result suits every project. We do not claim professional certification, physical mixing tests or validation for every supplier, device or site.

Worked examples

Concrete: a 10 × 10 ft slab

At 4 in depth: 10 × 10 × (4 ÷ 12) = 33⅓ ft³ net. With 10% waste: 36⅔ ft³, or about 1.36 yd³. Divide by 0.60 ft³ per 80 lb QUIKRETE 1101 bag: 61.111… rounds up to 62 bags. Concrete and Concrete Bags use the same answer for these inputs.

Gravel: a compacted 2 × 3 m bed

At 0.1 m depth, net volume is 0.6 m³. With an entered multiplier of 1.2 and 10% waste: 0.6 × 1.2 × 1.1 = 0.792 m³. At an entered loose density of 1,600 kg/m³, that is 1,267.2 kg. Dividing by a 25 kg bag gives 50.688, so buy 51 bags.

Block: a 10 × 8 ft wall

With no openings and a nominal 16 × 8 in face: 80 ÷ (128 ÷ 144) = 90 installed equivalents. A 5% block allowance gives 94.5, so buy 95 blocks individually. If matching reference premix is selected, 90 × 1.10 ÷ 13 = 7.615… rounds up to 8 bags. Without a mortar selection, the estimate stays incomplete.

Change log

Confirmed calculation corrections will be dated here. Publication dates are set when changes are released.