All calculators convert your inputs to feet first, compute the volume or area, then convert to the units you buy in. Nothing is rounded until the final result; bag and can counts are always rounded up.

Unit conversions

• 1 cubic yard = 27 cubic feet
• 1 cubic meter = 35.3147 cubic feet
• 1 inch = 1/12 ft · 1 yard = 3 ft · 1 meter = 3.2808 ft
• 1 short ton = 2,000 lb

Volume

• Rectangle: length × width × depth
• Circle or round column: π × (diameter ÷ 2)² × depth

Concrete

Volume × (1 + waste %) gives the amount to order. Pre-mixed bag yields (QUIKRETE published figures):

Gravel and stone

Tons = cubic yards × density. Typical loose densities we use (these vary with stone type and moisture, so use your supplier's figure if they give one):

Dirt and topsoil

Cubic yards = volume × (1 + settling %) ÷ 27; tons = cubic yards × density. Loose soil settles after placement, so we default to 20% for fill dirt and 10% for topsoil. Typical dry densities:

Bagged topsoil counts use 0.75, 1, 1.5 cu ft bags (a 40 lb bag is about 0.75 cu ft).

Mixing concrete from cement

A 94 lb bag of Portland cement is 1 cu ft. Dry ingredients = finished volume × 1.54, split by the mix ratio (by volume). Water is estimated at a 0.5 water–cement ratio by weight (8.34 lb per gallon).

• 1:2:3 — slabs, driveways, footings
• 1:2:4 — general purpose
• 1:3:6 — lean fill, non-structural

Board feet

Board feet = thickness (in) × width (in) × length (ft) ÷ 12. One board foot is 144 cubic inches.

Slope

From two points: m = (y₂ − y₁) ÷ (x₂ − x₁), b = y₁ − m·x₁, angle = arctan(m). From rise and run: grade % = rise ÷ run × 100, angle = arctan(rise ÷ run), ratio = 1 : (run ÷ rise), pitch = rise per 12 of run.

Asphalt and sand

Hardened concrete: about 145 lb per cu ft normal weight, 115 lightweight (STRUCTURE magazine). Compacted hot-mix asphalt: 145 lb per cu ft. Dry sand: 1.35 tons per cubic yard (published figures range 1.2–1.38); a 50 lb bag of play sand holds about 0.5 cu ft.

Pavers: 6 in of crushed-stone base for patios and walkways (10 in or more for driveways) under 1 in of bedding sand, from Unilock's installation guide. Base gravel uses the crushed-stone density above.

Masonry

Concrete block: a 16 × 8 in face including the joint, so 1.125 blocks per sq ft; one 80 lb bag of mortar mix lays about 13 blocks. Brick: bricks per sq ft = 144 ÷ ((length + 0.375) × (height + 0.375)); about 7 bags of masonry cement and 1 ton of sand per 1,000 bricks.

Rebar

Bars each way = (side − 2 × edge clearance) ÷ spacing + 1. Nominal weights (ASTM A615): #3 0.376 lb/ft, #4 0.668 lb/ft, #5 1.043 lb/ft.

Drywall

Area = walls (+ ceiling) without subtracting openings. Per sq ft of board: 0.009 gal joint compound, 0.35 ft tape, 1.25 screws (Lowe's estimator).

Carpet

Strips = room width ÷ roll width, rounded up; each strip is the room length + 6 in for trimming. We try both directions and use the shorter roll length. Pad = room area.

Sod and grass seed

Sod pallets default to 450 sq ft. New-lawn seeding rates (NC State Extension), halved for overseeding:

Lawn fertilizer

Pounds of product = area ÷ 1,000 × lb of nitrogen per 1,000 sq ft ÷ (N% ÷ 100), where N% is the first number on the bag. Phosphate and potash applied = product × their percentages. Default rate 1 lb N per 1,000 sq ft, the usual ceiling for one application of quick-release nitrogen (Rutgers fact sheet FS839).

Lumber

Pieces per board = (board length + kerf) ÷ (cut length + kerf), rounded down; boards = pieces ÷ pieces per board, rounded up. Default kerf 0.125 in. Board feet use the nominal size (a 2×4 counts as 2 × 4 in); the 3D board uses the actual size:

Plant spacing

Square grid: plants = area ÷ spacing². Staggered (triangular) rows: each plant covers spacing² × √3⁄2 (0.866), so the same area takes about 15% more plants, and rows sit 0.866 × spacing apart. Counts are rounded up and ignore edge effects.

Electrical load

NEC 220.82 optional method for a single-family home on a 120/240 V service of 100 A or more: 3 VA per sq ft of living area, 1,500 VA per small-appliance and laundry circuit and the nameplate rating of fixed appliances; the first 10,000 VA count in full and the rest at 40%. Then add the largest of the air conditioner or heat pump at 100%, electric heat at 65% (fewer than four thermostats) or 40% (four or more), or a heat pump plus 65% of its backup strips. Amps = total VA ÷ 240 V; service = the next of 100, 125, 150, 200, 300, 400 A. An estimate for planning: the permit calculation is the electrician's.

Fence

Posts = length ÷ spacing (rounded up) + 1. Concrete per post = (π × (hole ÷ 2)² − post width²) × hole depth, in 80 lb bags of 0.6 cu ft.

Area: acres and square yards

1 acre = 43,560 sq ft; 1 square yard = 9 sq ft; 1 m² = 10.7639 sq ft; 1 hectare = 10,000 m². Triangles use ½ × base × height.

Landscape stone and fill

Bagged pea gravel and river pebbles: 0.5 cu ft per bag. Fill dirt truck loads assume 12 cu yd per load.

Tons to cubic yards divides by the same densities as above; asphalt and concrete use 145 lb per cu ft × 27 ÷ 2,000.

Mulch and compost

Volume = area × depth. Mulch bags: 2 and 3 cu ft; default depth 3 in (Iowa State Extension: 3–4 in around trees and shrubs on well-drained soil, 2–3 in on heavy soil). Compost default layer 3 in for new beds; Oregon State Extension gives 3–4 in for new beds, ¼–1 in a year for existing beds and 1–2 in before a new lawn. Compost bags use the topsoil bag sizes. Raised beds: inside length × width × soil depth × beds, plus settling (topsoil allowance); compost share up to 25% by volume (Oregon State: never compost alone).

Epoxy

Gallons = cubic inches × (1 + extra) ÷ 231; default extra 10% for the mixing cup, edges and drips (a convention). Resin and hardener split by the volume ratio on the kit.

Shingles

Roof area = footprint at the eaves × √(1 + (pitch ÷ 12)²), the same for gable and hip roofs of one pitch. Bundles = area × (1 + waste) ÷ 100 × bundles per square (default 3, GAF Timberline HDZ at 33.33 sq ft per bundle), rounded up; default waste 10% (Roofr gives 10–15%). Starter strip and drip edge = eaves + rakes; starter bundles at 120 ft (GAF Pro-Start). Hip roofs: ridge = long side − short side, each hip = √(2 × (width ÷ 2)² + rise²).

Roofing and roof pitch

Squares = roof area (as for shingles) × (1 + waste) ÷ 100. Underlayment rolls = squares × 100 ÷ 1,000 (GAF FeltBuster; laps come out of the waste allowance). Ice barrier rolls = eave length × courses × 3 ft ÷ 200 (GAF WeatherWatch). Pitch = 12 × rise ÷ run; angle = arctan(pitch ÷ 12). Asphalt shingles need at least 2/12 and double underlayment below 4/12 (IRC R905.2.2).

Siding

Net area = 2 × (length + width) × wall height + gables (½ × width × width ÷ 2 × pitch ÷ 12 each) − windows × 15 − doors × 20 sq ft. Squares = net × (1 + waste) ÷ 100; boxes at 200 sq ft, rounded up; default waste 10% (a convention).

Decking

Rows = (deck width + gap) ÷ (board width + gap), rounded up; boards = rows × boards per row × (1 + waste). Defaults: 5.5 in boards (5/4×6 and 2×6 actual), 3/16 in gap (Trex: 3/16–3/8 in), joists 16 in on center (an editable default; the decking maker or IRC Table R507.7 sets the maximum), 2 screws per board per joist (IRC R507.7 minimum), 10% waste. Joists, beams and footings are not sized.

Baseboard

Linear feet = 2 × (length + width) − doors × door width (default 3 ft). Pieces = linear feet × (1 + extra) ÷ piece length (8, 12, 16 ft), rounded up; default extra 10%.

Retaining walls

Courses = exposed height ÷ block height (rounded up) + 1 buried course; blocks per course = length ÷ block face length. Base and drainage gravel are length × width × depth at the crushed-stone density. Their default sizes are typical values, not a design; follow the block manufacturer's guide.

Stairs

Risers = total rise ÷ maximum riser, rounded up; riser height = total rise ÷ risers; treads = risers − 1. Code check against IRC R311.7.5: riser ≤ 7.75 in, tread ≥ 10 in. Lengths are shown to the nearest 1/16 in.

Cut stringers: length = risers × √(riser² + tread²); wood left under each notch = board depth − riser × tread ÷ √(riser² + tread²); the bottom riser is cut down by one tread thickness. From AWC DCA 6: 2×12 minimum (11.25 in deep), at least 3 cut stringers, no more than 18 in apart on stairs wider than 36 in, a landing above 12 ft of rise; DCA 6 analyzed cut 2×12s at 5.1 in of remaining depth, and the calculator flags less.

Grout

Pounds per sq ft = 144 ÷ ((L + j)(W + j)) × ((L + j)(W + j) − L·W) × depth × 0.064, in inches. 0.064 lb per cubic inch is back-calculated from CUSTOM's Polyblend sanded grout coverage chart and matches it within a few percent.

Pool salt

Pounds = gallons × 8.34 × (target − current ppm) ÷ 1,000,000. Default target 3,200 ppm.

Pool chlorine

Pounds of available chlorine come from the pool salt formula, then are divided by the product's strength. Liquid strengths are read as grams of chlorine per 100 mL; household bleach labels give sodium hypochlorite by weight, which comes out within a few percent of that. Default target 3 ppm free chlorine (CDC: at least 1 ppm in pools, 2 ppm with stabilized chlorine). Default strengths, editable on the page:

Solar panels

System size (kW) = yearly use to cover ÷ yearly output per kW for the state; panels = kW × 1,000 ÷ panel watts, rounded up. Output per kW and peak sun hours come from NREL PVWatts v8 (developer.nlr.gov), NSRDB TMY for each state's largest city, fetched 2026-10-30: azimuth 180° (south), tilt 20°, fixed roof mount, standard modules, 14% system losses. The full table is on the solar panel calculator page.

Metal weight

Weight per foot = cross-section (sq in) × 12 × density; density in lb per cubic inch = g/cm³ × 0.0361273. Tube sections are outside minus inside (square corners). Densities from the Engineers Edge table:

Insulation

R-value to add from ENERGY STAR's table for the climate zone (attic with no insulation, attic with 3–4 in already, floor over unheated space). Blown insulation: settled depth = R-value ÷ R-value per inch, using blown-in fiberglass 3, blown-in cellulose 3.7 from the Owens Corning AttiCat and U.S. GreenFiber coverage charts (editable; the bag's chart wins). Batts are sold by R-value, so the calculator names one or two standard batts (R-13, R-19, R-30, R-38) that add up to the target.

Furnace size

Heat needed = heated sq ft × BTU per sq ft for the climate zone (zone 1 30–35, zone 2 35–40, zone 3 40–45, zone 4 45–50, zone 5 50–60, zone 6, 7 or 8 50–60; InspectApedia, consistent with Bryant's 30–35 warm and 50–60 cold). No published figure exists for zones 6–8, so they use zone 5's range. Low end of the range for a well-insulated house, middle for average, high end for a drafty one. Furnace input = heat ÷ AFUE (default 95%), rounded up to the next 20,000 BTU, minimum 40,000. An estimate only; a Manual J load calculation decides the real size.

Air conditioner size

ENERGY STAR room air conditioner chart (8 ft ceilings), then shaded -10% / very sunny +10%, +600 BTU per person beyond two, +4,000 BTU in a kitchen.

Paint

Wall area = 2 × (length + width) × height, minus 20 sq ft per door and 15 sq ft per window. Gallons = area × coats ÷ coverage. Default coverage is 350 sq ft per gallon, the low end of the 350–400 range printed on most cans. We suggest whole gallons plus quarts for the remainder, and a full gallon instead of 3 quarts. Remainders under 0.05 gallon (about 6 fl oz) are dropped.

Testing

Each calculator has automated tests with hand-worked answers, run before every update. The worked example on each calculator page is one of those tests, so the page and the tool can't disagree.