How We Calculate

Slab volume: cubic yards = (length × width × thickness ÷ 12) ÷ 27. Thickness in inches is divided by 12 to convert to feet. All three dimensions are multiplied to get cubic feet. Dividing by 27 converts to cubic yards; there are exactly 27 cubic feet in one cubic yard.

Post hole volume: cubic feet = π × (diameter ÷ 24)² × (depth ÷ 12). Diameter in inches is halved to get radius, divided by 12 to convert to feet, then squared. Result is multiplied by depth in feet and by π.

Bag yields are taken from published manufacturer specifications: an 80 lb bag covers 0.60 cu ft; a 60 lb bag covers 0.45 cu ft; a 40 lb bag covers 0.30 cu ft. Bag counts always round up, never down, because running short mid-pour creates a cold joint that permanently weakens the slab.

Waste factor: 10% is added to all results. This is standard contractor practice to account for uneven subgrade, form overflow, and mixing loss.

Mix design minimums: ACI 318 (Building Code Requirements for Structural Concrete) sets 2500 PSI as the minimum compressive strength for residential slabs and footings. Driveways and garage floors exposed to freeze-thaw cycles require 3000–3500 PSI. Full design strength is reached at 28 days; concrete achieves approximately 70% of design strength at 7 days under standard moist-curing conditions (Type I/II Portland cement). Do not load slabs or remove forms before the 7-day minimum.

See: Concrete Calculator, Concrete Slab Calculator, Concrete Driveway Calculator

Volume formula: cubic yards = (length × width × depth ÷ 12) ÷ 27. Identical to the concrete slab formula. Depth in inches is divided by 12, all three dimensions are multiplied for cubic feet, then divided by 27.

Weight conversion: tons = cubic yards × material density. Density values are industry averages: crushed gravel 1.40 t/yd³, pea gravel and river rock 1.35 t/yd³, crushed limestone and granite 1.50 t/yd³. Actual delivered weight varies by moisture and supplier. If your supplier gives you a per-yard weight, use that figure instead.

Waste factor: 10% is added for edge losses, uneven spreading, and compaction. Uncompacted gravel can settle 10–15% over the first season; proper compaction with a plate compactor reduces ongoing settling to near zero.

See: Gravel Calculator, Driveway Gravel Calculator, Pea Gravel Calculator

Unit conversions use exact multipliers: 1 square yard = 9 square feet; 1 square meter = 10.7639 square feet. Waste factors for flooring default to 10% for straight-lay installations and should be increased to 15% for diagonal or pattern installs.

See: Square Footage Calculator, Room Square Footage Calculator

Volume formula: cubic yards = (length × width × depth ÷ 12) ÷ 27. Identical to the gravel formula. Depth in inches is divided by 12 to convert to feet before multiplying dimensions.

Bag conversion: total cubic feet = cubic yards × 27. Divide by the bag size (standard bags are 2 cu ft) and round up. One 2 cu ft bag covers 24 sq ft at 1 inch deep or 12 sq ft at 2 inches deep.

Waste factor: 10% added for settling. Freshly spread mulch compresses over the first season. The 10% buffer also covers uneven terrain and edge spillage.

See: Mulch Calculator, How Much Mulch Do I Need, Mulch Bags Calculator

Volume formula: cubic yards = (length × width × depth ÷ 12) ÷ 27. Same formula as gravel and mulch.

Settling factor: 15% is added for topsoil, higher than the 10% used for gravel. Topsoil contains organic matter that compresses more than aggregate under its own weight and foot traffic.

Bag conversion: total cubic feet = cubic yards × 27. Divide by bag size (typically 1 cu ft or 0.75 cu ft) and round up.

See: Topsoil Calculator, Topsoil in Cubic Yards, Raised Bed Topsoil Calculator

Area formula: square feet = length × width. Square yards = square feet ÷ 9. (Used for carpet pricing, which retailers quote per square yard.)

Waste factor: 10% for straight-lay rectangular rooms; 15% for diagonal or herringbone patterns and rooms with many obstacles (islands, fireplaces, alcoves). Applied before box count calculation.

Box count: boxes = ⌈(area × waste factor) ÷ coverage per box⌉. Coverage per box is printed on the carton label. Always round up; you cannot install a fraction of a box.

See: Flooring Calculator, Laminate Calculator, Vinyl Plank Calculator, Hardwood Calculator

Tile count formula: tiles = ⌈(room area × waste factor) ÷ (tile width × tile length ÷ 144)⌉. Tile dimensions in inches are divided by 144 to convert square inches to square feet. The result is divided into the total area (with waste) and rounded up.

Waste factor: 10% for straight grid layouts; 15% for diagonal (45°) or complex patterns; 20% for high-end tile or rooms with many cutouts (niches, drains, posts).

Box count: boxes = ⌈tiles ÷ tiles per box⌉. Tiles per box varies by manufacturer. Enter the actual box count from the product label for an exact result.

See: Tile Calculator, Bathroom Tile Calculator, Floor Tile Calculator, Shower Tile Calculator

Wall area formula: wall area = (room perimeter × ceiling height) − (doors × 20 sq ft) − (windows × 15 sq ft). Standard door deduction is 20 sq ft; standard window is 15 sq ft. These are typical values; adjust for oversized openings.

Gallons per coat: gallons = ⌈wall area ÷ 350⌉. 350 sq ft per gallon is the industry standard coverage rate. Highly porous or previously unpainted surfaces may require more paint per gallon. Manufacturer-stated coverage (usually 400 sq ft) assumes ideal conditions; 350 is the practical rate.

Coat count: two coats is standard. One coat over a similar color for touch-ups; two coats for full repaints and color changes. All calculators default to two coats.

See: Paint Calculator, Exterior Paint Calculator, Room Paint Calculator

R-value formula: total R = R-value per inch × installed depth in inches. Common values: blown cellulose 3.7 per inch; blown fiberglass 2.5 per inch; fiberglass batts 3.14 per inch; spray foam (closed-cell) 6.5 per inch. Values sourced from DOE/ORNL Building Envelope Research.

Bag count: bags = ⌈area ÷ coverage per bag at target depth⌉. Coverage per bag at a given depth is printed on every bag label. This figure changes with depth; a bag that covers 40 sq ft at 4 inches covers only 20 sq ft at 8 inches.

Waste factor: 10% is added for blown-in insulation to account for bag measurement variation and coverage inconsistency at the blower nozzle. Note that settled depth may be 10–20% less than installed depth within the first year; always plan to top up after the first winter.

DOE recommended R-values by climate zone: Zone 1–2 (FL, TX Gulf Coast): R-30 attic, R-13 wall. Zone 3–4 (TN, VA, OR): R-38 attic, R-13+5 wall. Zone 5–6 (NY, CO, MN): R-49 attic, R-15+5 wall. Zone 7–8 (AK, northern MN): R-60 attic, R-21+5 wall. Values sourced from DOE Building Technologies Office (energy.gov) energy efficiency guidelines.

See: Insulation Calculator, Attic Insulation Calculator, Blown-In Insulation Calculator, R-Value Calculator

Wall area: sum of (width × height) for each wall, then subtract doors (20 sq ft each) and windows (15 sq ft each). Ceiling area = room length × room width.

Sheet count: sheets = ⌈total area × 1.10 ÷ sheet area⌉. A standard 4×8 sheet covers 32 sq ft; a 4×10 covers 40 sq ft; a 4×12 covers 48 sq ft. 10% waste is standard for residential rooms. Increase to 15% for rooms with many cut-outs or vaulted ceilings.

Joint compound: approximately 0.053 gallons per square foot of finished drywall area, covering three coats (tape, first, finish). A standard 4.5-gallon bucket covers roughly 85 square feet of drywall.

Screws: approximately 1 screw per square foot of drywall. Screws are spaced 12 inches apart on ceilings and 16 inches on walls per GA-216 Gypsum Board Application standard.

See: Drywall Calculator, Drywall Cost Calculator, Drywall Sheet Calculator, Drywall Mud Calculator

Volume formula: cubic yards = (length × width × depth ÷ 12) ÷ 27. Identical to the gravel and mulch formula. For circular areas: cubic yards = π × (diameter ÷ 2)² × (depth ÷ 12) ÷ 27.

Weight conversion: tons = cubic yards × material density. Density values by sand type: play sand 1.35 t/yd³, paver base sand 1.50 t/yd³, concrete sand 1.52 t/yd³, all-purpose sand 1.40 t/yd³. These are dry bulk densities. Wet sand can weigh 15–30% more depending on saturation level.

Bag count: bags = ⌈(cubic feet × 1.10) ÷ 0.5⌉. A standard 50 lb bag of sand fills approximately 0.5 cubic feet. Bag count always rounds up.

Waste factor: 10% added for spillage and compaction.

See: Sand Calculator

Volume formula: cubic feet = length × width × (depth ÷ 12). Depth in inches is divided by 12 to convert to feet.

Weight formula: tons = (cubic feet × density in lbs/ft³) ÷ 2000. Density values: hot mix asphalt (HMA) 145 lbs/ft³; asphalt millings 110 lbs/ft³; cold patch 100 lbs/ft³. These are typical industry averages; actual density varies by mix design and compaction.

Waste factor: 10% is added to raw tonnage for paving. Asphalt is ordered in whole-ton increments; suppliers round up to the nearest ton at the plant.

See: Asphalt Calculator

Board foot formula: board feet = (thickness × width × length) ÷ 12. Dimensions use nominal (stated) inches for thickness and width, and feet for length. A 2×4×8 board = (2 × 4 × 8) ÷ 12 = 5.33 board feet. This is the standard lumber industry formula. The NHLA uses it for hardwood grading; the same calculation applies across all lumber types including framing lumber.

Weight formula: lbs = total board feet × lbs per board foot by species. Species weight values (lbs/BF): SPF (spruce-pine-fir) 2.3, Douglas fir 2.6, Southern yellow pine 2.7, white pine 2.4, poplar 2.7, red oak 3.8, white oak 3.9, hard maple 4.0, cherry 3.1, black walnut 3.5. Values derived from published green-wood specific gravity data (USDA Forest Products Laboratory Wood Handbook).

No waste factor is applied to lumber, as board feet measure nominal dimensions and waste depends entirely on the specific cuts required for the project.

See: Lumber Calculator, Board Foot Calculator

The "+ 1" in the post formula accounts for the final end post on a straight run. Picket gap can be negative for board-on-board fencing where boards overlap; the formula uses the effective spacing (picket width + gap), which must remain greater than zero.

Post hole depth (1/3 rule): in-ground depth = above-ground height × 12 ÷ 2. The recommended depth is the greater of the 1/3 rule result, the local frost depth + 6 inches, or 24 inches minimum. The frost rule requires posts to extend at least 6 inches below the frost line to prevent heave. Frost depth ranges from 0 inches in Zone 1 (deep south FL/TX) to 60+ inches in northern Minnesota. International Residential Code (IRC) Section R403.1.4 requires footings to extend below the local frost depth for frost-susceptible soils. Check your local building department for the required depth before setting posts.

Chain link: line posts = sections − 1, where sections = ⌈fence length ÷ post spacing⌉. Fabric rolls = ⌈fence length ÷ 50⌉ (standard 50-ft rolls). Top rail sections = ⌈fence length ÷ 10⌉ (standard 10-ft sections).

See: Fence Calculator, Fence Post Depth Calculator, Chain Link Fence Calculator

ICPI (Interlocking Concrete Pavement Institute) paver sand base and joint sand standards will be added when paver calculators go live. Spotted an incorrect citation? Let us know.

Cost ranges shown in our calculators are national averages collected from major home improvement retailers and regional ready-mix suppliers. Prices are reviewed quarterly and were last verified in June 2026. Always confirm current pricing with local suppliers before ordering.

Bulk material prices for gravel and ready-mix concrete depend heavily on your distance from the quarry or plant. Treat all price estimates as planning baselines, not supplier quotes. Always confirm current pricing locally before ordering.

Our calculators produce estimates, not engineered specifications. For structural concrete work (foundations, load-bearing walls, retaining structures), consult a licensed structural engineer. Local building codes, soil conditions, and climate can require different specifications than a general-purpose calculator can anticipate.

All results should be verified with your material supplier before ordering. Suppliers can account for local aggregate density, mix design variations, and delivery minimums that no online calculator can predict.