Concrete and project math, done in your browser

You can check every answer HomeMath gives: it follows published standards, handles the cases where concrete calculators can disagree by a stated rule, and is tested against answers worked out by hand.

The standards HomeMath follows

• US customary units. HomeMath works in feet, inches and cubic yards: 12 inches make a foot, 3 feet a yard, so a cubic yard is 3 × 3 × 3 = 27 cubic feet. Ready-mix concrete is sold by the cubic yard in the US, so every US volume ends there. Source: US customary units.
• Metric conversion. In metric, HomeMath converts by the exact definitions of the 1959 international yard and pound agreement: a yard is 0.9144 m, so an inch is 2.54 cm and a foot 0.3048 m, and a pound is 0.45359237 kg. A cubic yard is then 0.7646 m³, and a cubic meter 1.31 cubic yards. Source: International yard and pound.
• Premixed bag yields. HomeMath counts bags by the yield printed on US concrete mix bags: 0.30 cubic feet for a 40 lb bag, 0.45 for a 60 lb bag and 0.60 for an 80 lb bag, so a cubic yard takes 90, 60 or 45 bags. Quikrete's data sheet also lists a 50 lb bag at 0.375 and a 90 lb bag at 0.675 cubic feet. In metric it also counts your own kilogram bag by the yield in liters on its label, with no default, because brands differ. Source: Quikrete Concrete Mix, data sheet.
• Concrete weight. HomeMath weighs concrete at 150 lb per cubic foot, 4,050 lb a cubic yard: Dumpsters.com's figure for a solid slab and Inch Calculator's for a typical mix, which puts standard concrete at 3,700–4,220 lb a cubic yard and lightweight concrete at 2,360–3,120. Quikrete gives its bagged Concrete Mix a unit weight of about 140 lb per cubic foot freshly mixed (ASTM C138). Rebar adds its own weight per foot. Source: Dumpsters.com, concrete weight calculator, Inch Calculator, concrete weight calculator, Quikrete Concrete Mix data sheet.
• Concrete mix ratios. HomeMath mixes by volume: the dry materials take 54% more room than the concrete they make (× 1.54, Inch Calculator; the US Navy's builder manual uses 41 to 42 cu ft of dry materials per cubic yard, × 1.52 to 1.56), split by the ratio's parts. A 94 lb sack of Portland cement is about 1 cu ft loose (Navy manual). 1:2:3 is Quikrete's recipe with its Portland cement; Inch Calculator's grades run from 1:5:10 (725 psi) to 1:1:2 (3,625 psi), with water-cement ratios of 0.40 to 0.60 at most. Sand and gravel are weighed at their published loose weights (dry sand, #57 stone). Source: Inch Calculator, concrete mix calculator, Quikrete Portland Cement, Navy builder manual, cement, material estimates.
• Rebar sizes and mesh. HomeMath weighs US rebar by its size table: #3 0.375 in, 0.376 lb per foot; #4 0.5 in, 0.668 lb per foot; #5 0.625 in, 1.043 lb per foot (the number is the diameter in eighths of an inch). Its starting cover (3 in), lap (40 bar diameters), stick (20 ft) and chair spacing (4 ft) are HomeMath's assumptions for you to replace with your plans'. Welded wire mesh is 6 × 6 in W1.4 × W1.4 in 5 × 10 ft sheets or 5 × 150 ft rolls, overlapped one 6 in square. Source: Wikipedia, rebar sizes, Ernest Maier, wire mesh roll.
• Self-leveler coverage. HomeMath counts self-leveler bags by their yield. Quikrete's Self-Leveling Floor Resurfacer yields 0.45 cu ft a 50 lb bag (21 sq ft at 1/4 in) with about 5 quarts of water, and goes from a featheredge to 5/8 in a layer on a primed floor. CustomTech's TechLevel 150 covers 45.98–48.19 sq ft at 1/8 in (0.48–0.50 cu ft a bag) and pours up to 1 1/2 in at once. The calculator starts at 0.5 cu ft; your bag's label is the final word. Source: Quikrete Self-Leveling Floor Resurfacer data sheet, CustomTech TechLevel 150.
• Concrete masonry unit sizes. HomeMath counts the standard 8 × 8 × 16 in block: its nominal size includes a 3/8 in mortar joint, the block itself is 7 5/8 × 7 5/8 × 15 5/8 in. Its cores are sized from ASTM C90's 1 1/4 in minimum face shell and a 1 in web, HomeMath's assumption for a typical block (C90 itself sets a 3/4 in minimum web). Metric blocks differ by country, so in metric the calculator takes the block's face with its joint in millimeters. Its presets are the usual blocks there, 440 × 215 mm in the UK and Ireland and 390 × 190 mm in Australia, New Zealand and Canada, each with a 10 mm joint (HomeMath's assumption, like the US 3/8 in), which lay 9.88 and 12.50 per m². Their core fill comes from the maker's data sheet. Source: Concrete masonry unit, ASTM C90.
• Mortar bag coverage. HomeMath counts mortar bags by Quikrete Mortar Mix's data sheet: one bag lays about 12 standard 8 × 8 × 16 in blocks (80 lb), 9 standard 8 × 8 × 16 in blocks (60 lb), 6 standard 8 × 8 × 16 in blocks (40 lb). Other mortars differ, so the field takes the number on your bag. Source: Quikrete Mortar Mix data sheet.
• Published price ranges. HomeMath's price ranges are US figures read in October 2026, each from a named source: ready-mix at $160–$195 a cubic yard (2025 average $179.95) and the NRMCA history, installed slabs, patios, driveways, asphalt driveways and stamped finishes per square foot from Concrete Network (pages updated or reviewed January to July 2026), and walkways from its walkway cost page (updated May 2020); short-load delivery and pump rental from Fixr (updated January 2025); labor per square foot from Inch Calculator (updated July 2023). They are national ranges, not quotes, and the price fields stay yours to change. Source: Concrete Network, concrete prices, stamped concrete cost, patio cost, driveway cost, walkway cost, Fixr, concrete delivery cost, Inch Calculator, concrete slab cost.
• Removal, weight and hauling. HomeMath prices tearing out a slab at Fixr's $2–$4 per square foot for plain concrete and $4–$6 with rebar or wire mesh, disposal included (updated January 2025). It weighs the debris at Dumpsters.com's 150 lb per cubic foot of solid concrete (4,050 lb a cubic yard) and fills its 10 yard dumpster for concrete to the 10 ton weight limit, at $300–$795 a rental. The do-it-yourself jackhammer is Lawn Love's $91 for 24 hours (updated October 2026). Source: Fixr, concrete removal cost, Dumpsters.com, concrete disposal, concrete weight calculator, Lawn Love, concrete removal cost.
• Gravel weights and prices. HomeMath weighs gravel, stone, sand and soil by published loose weights per cubic yard: pea gravel 1.25–1.50 tons, #57 or 3/4 in crushed stone 1.40–1.70 tons, base gravel (crusher run, #411, ABC) 1.40–1.70 tons, #3 stone (1–2 in) 1.40–1.70 tons, river rock 1.30–1.60 tons, sand (dry) 1.30–1.50 tons, topsoil (dry) 1.00–1.30 tons, from Inch Calculator (river rock from Stone Center), and calculates with the middle of each range unless you type your supplier's figure. Prices per ton and per cubic yard, read in October 2026, are Lawn Love's for pea gravel, its bags and truckloads (updated October 2026), Fixr's landscaping stones page for river rock (updated January 2025) and Fixr's gravel driveway page for #57, #3 and crusher run, its driveway layers and costs (updated August 2022). They are national material prices before delivery, not quotes. Source: Inch Calculator, cubic yards to tons, gravel calculator, Stone Center, Lawn Love, pea gravel cost, Fixr, landscaping stones, Fixr, gravel driveway cost.
• Post holes, fast-setting bags and tube forms. HomeMath sizes a post hole by Quikrete's setting-posts sheet: 3 times the post's width, as deep as 1/3 of the post's overall length plus 6 in of gravel or crushed stone at the bottom, and below the frost line for a structural post. It takes the post out of the concrete at its actual size, 3.5 × 3.5 in for a 4x4 and 5.5 × 5.5 in for a 6x6 (the American Softwood Lumber Standard's dressed sizes). Quikrete Fast-Setting Concrete yields about 0.375 cu ft per 50 lb bag, by its data sheet. Tube forms are Sonoco's Sonotube sizes: Builder's Tube in 6, 8, 10, 12 in, 4, 8, 12 ft long, and round forms from 6 to 36 in; their diameters are nominal. Source: Quikrete, setting posts, Quikrete Fast-Setting Concrete data sheet, Sonotube Builder's Tube, Sonotube round forms, Lumber sizes.
• Paver base depths and coverage. HomeMath starts a paver base at 4 in of compacted gravel under a patio or walkway (Concrete Network: 4 to 6 in, 4 in working well for a patio) and 6 in under a driveway (Inch Calculator: 6 to 8 in), adds 20% for compaction (Inch Calculator) and a 1 in sand bed. Paver base bags hold 0.5 cu ft (Quikrete HardScapes), and a 50 lb bag of SEK Surebond's PolySweep joint sand fills 50–75 sq ft at up to 1/4 in, 25–50 sq ft at 1/4–1/2 in, 15–25 sq ft at 1/2–3/4 in joints. Source: Concrete Network, paver base, Inch Calculator, paver base calculator, Quikrete HardScapes paver base, SEK Surebond PolySweep.
• Paver prices. HomeMath prices a paver job by Lawn Love's paver patio guide (updated December 2025): the pavers alone at $4–$6 per square foot for concrete pavers, $4–$8 per square foot for brick pavers, $7–$16 per square foot for natural stone, $13–$30 per square foot for flagstone, plus labor at $5–$15 per square foot, and permeable pavers at Bob Vila's installed $10–$40 (April 2024). The whole-job ranges, patio $8–$24, walkway $13–$27, driveway $10–$40 per square foot for any paver, are Lawn Love's patio and walkway guides (the walkway guide updated October 2026), and so are the do-it-yourself bag and compactor prices. A walkway is priced at the walkway guide's installed figure for its paver (concrete pavers $7–$16, clay brick pavers $10–$19, natural stone pavers $13–$36), and a driveway, or a walkway of a paver that guide doesn't list, at the job's range for any paver, with the paver at its own price beside it. They are national ranges read in October 2026, not quotes. Source: Lawn Love, paver patio cost, paver walkway cost, Bob Vila, permeable pavers cost.
• Paver counts, waste and weight. HomeMath counts pavers as the area ÷ the face of one paver with its joint, rounded up, as Inch Calculator's paver calculator does, and adds the waste Inch Calculator's layout patterns page gives: 10% for running bond, 10% for basket weave, 10% for 90° herringbone, 20% for 45° herringbone. A pallet holds 78 to 160 sq ft of pavers by Inch Calculator, so without your supplier's figure the pallets are a range. Concrete Network gives 2 3/8 in pavers for residential patios and driveways and 3 1/8 in for streets; a paver's weight is its volume at 150 lb per cubic foot of solid concrete (Dumpsters.com). Source: Inch Calculator, paver calculator, layout patterns, Concrete Network, paver thickness.
• Drainage slope. HomeMath takes its slopes from Concrete Network's guide to exterior slabs: a minimum of 2%, a 1/4 in drop per foot, as a good rule, 1% (1/8 in per foot) often enough in a dry climate, and 3/8 in per foot in a wet one. For pavers it adds Unilock's figures: 1–2% away from a house as a common guideline, at most 2% for a patio and 5% for a walkway with a non-slip surface. The drop is the run × the slope; 1% is 0.12 in per foot. Source: Concrete Network, concrete slope, Unilock, pavers on a slope.
• Foundation and wall prices. HomeMath prices foundations by Fixr's installed ranges per square foot of footprint for each type (updated February 2026), poured retaining walls by Concrete Network's range for a basic wall per square foot of face (updated June 2020) beside Fixr's (updated January 2025), and block walls by Homewyse's mortared block wall (May 2026) and Fixr's block retaining walls, with Inch Calculator's prices for filled cores, stucco and the blocks themselves (updated August 2023). They are national ranges read in October 2026, not quotes. Source: Fixr, concrete foundation cost, Fixr, retaining wall cost, Concrete Network, concrete retaining wall cost, Homewyse, concrete block wall, Inch Calculator, concrete block wall cost.
• Footing minimums. HomeMath checks a strip footing against the International Residential Code's minimum size (R403.1.1): at least 12 in wide and 6 in thick, with a projection past the wall of at least 2 in and no more than the footing's thickness. The code's tables ask for wider footings under heavier houses and on weaker soil, and your local code and plans set the real size. Source: IRC R403.1 as adopted in Washington (WAC 51-51-0403).
• Segmental retaining walls. HomeMath builds a dry-stacked wall by Allan Block's gravity wall construction: a base trench 24 in wide with 6 in of wall rock (18 in and 4 in for walls under 4 ft), at least 6 in of buried block, and wall rock in the cores and 12 in behind the block, with a drain pipe over 4 ft or in silty or clay soil. Its block presets are Versa-Lok's 4 × 12 in Accent, 6 × 16 in Standard, 8 × 18 in Square Foot units. Source: Allan Block, gravity wall construction, Versa-Lok Standard (General Shale).

The edge cases HomeMath handles

• Thickness in inches: A 4 in slab is 4/12 = 0.333 ft thick, not 0.4 ft, and a 10 cm slab is 0.10 m. HomeMath converts inches to feet, and centimeters to meters, before it multiplies.
• Waste and spillage: The concrete, pad, cost, block, fence post, sonotube, concrete wall, concrete mix and self-leveling concrete calculators add 10% by default for uneven ground, form bulge and spillage, and show the volume without it too. Set it to 0 for the exact geometric volume. The driveway, patio and foundation cost calculators add a fixed 10% to the concrete to order. The gravel and gravel driveway calculators add an editable 10% extra, the paver base calculator 20% for compaction, the paver calculator the waste of the laying pattern (10% or 20%), and the rebar calculator 5% on the bar and mesh, all of which you can change.
• Gravel by weight: Quarries sell by the ton, projects are measured in yards. HomeMath turns yards into tons with each material's published weight per cubic yard, shows the answer at the whole published range, and lets you type your supplier's figure, since moisture and fines change it.
• Part bags: Bag counts always round up: 13.2 bags is 14 bags at the store.
• Ready-mix orders: The order line rounds the yards up to the next 0.25 yard, so a 2.1 yd pour is ordered as 2.25 yd, and in metric the cubic meters up to the next 0.25 m³. Ask your supplier for their own step and minimum load.
• Mixed units: Every length field takes feet, inches or yards, so 144 in, 12 ft and 4 yd give the same slab; in metric it takes meters or centimeters, so 300 cm and 3 m do too.
• US or metric: Each calculator switches between US units and metric. The math is the same either way: metric sizes are converted exactly (1 in = 2.54 cm), so 3.048 m gives the same slab as 10 ft. In metric, the bag counts add your own kilogram bag, counted by the yield in liters on its label, next to the US 40, 60 and 80 lb bags (and the 50 lb fast-setting bag in the fence post and sonotube calculators), and the block calculator counts your block from its face size in millimeters.
• Openings in block walls: HomeMath counts whole courses, a part course at the top included, then takes off the blocks the doors and windows leave out (1.125 per sq ft for the US block, or per m² for your block's face in metric). The waste allowance covers the cut blocks around them.
• Walls below ground: A wall starts below grade. The concrete wall calculator adds the strip footing under the wall and checks it against the code minimum, and the retaining wall block calculator adds the buried course (at least 6 in) to the courses you see, with the gravel base under it and the drainage gravel behind its full height.
• Replacing a slab: A replacement is two jobs: tearing out the old slab and pouring the new one. HomeMath's driveway and patio calculators add the removal of an old slab of the same size and thickness, priced by whether it holds rebar or mesh, and weigh its debris by its volume. An extension prices only the area you add.
• Prices: HomeMath knows no local prices. The slab price, driveway, patio, paver, removal, foundation and wall estimates and the cost pages use published national ranges, each with its source and date. The cost and block calculators' price fields start with round example numbers, and an estimate is only as good as the price you type.

How HomeMath is tested

HomeMath's volumes, bag counts and block counts are checked against answers worked out by hand. Every worked example and table on the site is computed with the same code the calculators run, so a page and its calculator can't disagree. If a result still looks wrong to you, send the link to the calculation to hello@homemath.app.