Calculation methodology
Every calculator on this site follows the same rules for measuring, converting, rounding and pricing. This page explains those rules and lists the default material values, with where they come from, so you can check any result and replace our defaults with your supplier’s or manufacturer’s figures.
Principles
- Material first, then purchase. Each result separates the exact amount the job needs, the allowance for waste, and what to buy once rounded to real package sizes.
- Your numbers win. Coverage, bag yield and weight fields accept the figure printed on your product or quoted by your supplier. Our defaults are typical values, not guarantees.
- Show the working. Every result lists the formulas with your numbers filled in, and the assumptions it used.
- Estimates only. The calculators estimate quantities and cost. They do not design structures, size footings or reinforcement, or check building codes.
Units and conversions
Calculations run internally in metric base units (meters, square meters, cubic meters, kilograms) at full precision, and are converted back to the units you chose only for display. US customary units use the exact international definitions:
| Unit | Equals | Definition |
|---|---|---|
| 1 inch | 2.54 cm | exact |
| 1 foot | 0.3048 m | exact |
| 1 yard | 0.9144 m | exact |
| 1 square foot | 0.09290304 m² | exact |
| 1 acre | 43,560 ft² | exact |
| 1 cubic yard | 27 ft³ = 0.764555 m³ | exact |
| 1 US gallon | 231 in³ = 3.785412 L | exact |
| 1 pound | 0.45359237 kg | exact |
| 1 US ton | 2,000 lb = 907.185 kg | exact |
Length boxes accept decimals (12.5), feet and inches (12' 6", 12 ft 6 in),
fractions (6 1/2") and metric values (350 cm). Entries that could mean two things,
such as 12 6, are rejected rather than guessed. Switching between US and metric converts the
values you entered; physical defaults such as paint coverage stay the same, so the answer does not change.
Rounding
- Display only. Numbers are rounded when shown (usually to two decimals), never in the middle of a calculation.
- Purchase quantities always round up to whole bags, boxes, cans or pieces, or to the supplier’s steps (such as ¼ cubic yard of ready-mix or ½ ton of gravel). A tiny tolerance stops floating-point noise, such as 2.0000000001 bags, from adding a unit.
- Leftovers are shown so you can see what the rounding costs you.
Waste and allowance
The allowance is a percentage added to the exact quantity before rounding: 10% turns 2.00 into 2.20. It covers cutting waste, breakage, spillage, uneven ground, and for loose materials, settling and compaction. Quick picks of 0%, 5%, 10% and 15% are offered; each calculator suggests a typical range. Cut-list tools (such as the linear feet calculator) also account for offcuts that are too short to reuse.
Concrete defaults
| Bag | Typical yield |
|---|---|
| 40 lb bag | 0.3 ft³ |
| 50 lb bag | 0.375 ft³ |
| 60 lb bag | 0.45 ft³ |
| 80 lb bag | 0.6 ft³ |
| 20 kg bag | 9.36 L |
| 25 kg bag | 11.71 L |
- Typical yield printed on standard concrete mix bags from major US manufacturers: 0.30 ft³ (40 lb), 0.375 ft³ (50 lb), 0.45 ft³ (60 lb), 0.60 ft³ (80 lb).
- Estimated from the same yield per kilogram as US bags (about 0.47 L per kg). Metric bag yields vary more by brand, so check the bag label.
- Most ready-mix suppliers take orders in quarter-yard (or quarter-cubic-meter) steps. Many have a minimum order and charge a short-load fee for small deliveries; ask your supplier.
- Common rule of thumb: bags are practical for small pours; around 1 cubic yard and above, ready-mix is usually easier and often cheaper.
- Normal-weight concrete is commonly taken as about 150 lb/ft³ (≈ 2,400 kg/m³) once placed.
Gravel and aggregate weights
| Material | Loose weight | Suggested allowance |
|---|---|---|
| General gravel (mixed sizes) | 1.4 tons/yd³ (1.66 t/m³) | 10% |
| Crushed stone (#57, 3/4 in clean) | 1.35 tons/yd³ (1.6 t/m³) | 10% |
| Pea gravel | 1.4 tons/yd³ (1.66 t/m³) | 5% |
| Road base / crusher run | 1.5 tons/yd³ (1.78 t/m³) | 15% |
Typical loose weights used by US aggregate suppliers and landscape yards (roughly 1.3–1.5 tons per cubic yard for most gravels). Your supplier’s weight per yard or per tonne is always more accurate. Small bags of gravel and stone at home centers are commonly 0.5 ft³ (about 14 L); check the bag, as sizes vary.
Paint defaults
| Value | Default |
|---|---|
| Wall paint coverage per coat | 350 ft² per gallon (8.6 m² per liter) |
| Primer coverage | 250 ft² per gallon (6.1 m² per liter) |
| Door | 20 ft² |
| Window | 15 ft² |
| US containers | 5-gallon bucket, 1-gallon can, 1-quart can |
| Metric containers | 10 L tin, 5 L tin, 2.5 L tin, 1 L tin |
- Most interior wall paints list 250–400 ft² per gallon per coat on the can; 350 ft² (≈ 8.6 m² per liter) is a common mid-range figure for smooth, previously painted walls.
- Primers typically list 200–300 ft² per gallon; 250 ft² (≈ 6.1 m² per liter) is used as a mid-range default.
- A standard interior door is about 3 ft × 6 ft 8 in (20 ft²); a typical window about 3 ft × 5 ft (15 ft²).
- Larger containers usually cost less per gallon/liter, so the purchase suggestion moves up a size when the smaller cans would nearly fill it.
Mulch, soil, sand and rock
Bulk landscaping materials are calculated by volume, then converted to weight with the typical loose densities below where a supplier sells by the ton or a bag is sold by weight.
| Material | Loose weight | Suggested allowance |
|---|---|---|
| Shredded hardwood | 0.3 tons/yd³ (0.36 t/m³) | 10% |
| Pine bark nuggets | 0.25 tons/yd³ (0.3 t/m³) | 5% |
| Dyed wood mulch (black, brown, red) | 0.3 tons/yd³ (0.36 t/m³) | 10% |
| Wood chips (arborist) | 0.25 tons/yd³ (0.3 t/m³) | 10% |
| Screened topsoil | 1.1 tons/yd³ (1.31 t/m³) | 15% |
| Garden soil (topsoil and compost blend) | 0.9 tons/yd³ (1.07 t/m³) | 15% |
| Compost | 0.6 tons/yd³ (0.71 t/m³) | 10% |
| Fill dirt | 1.2 tons/yd³ (1.42 t/m³) | 20% |
| All-purpose or fill sand | 1.35 tons/yd³ (1.6 t/m³) | 10% |
| Concrete sand (coarse) | 1.4 tons/yd³ (1.66 t/m³) | 10% |
| Mason sand (fine) | 1.3 tons/yd³ (1.54 t/m³) | 10% |
| Play sand | 1.3 tons/yd³ (1.54 t/m³) | 5% |
| River rock (1–3 in) | 1.35 tons/yd³ (1.6 t/m³) | 5% |
| Decorative crushed stone (3/8–3/4 in) | 1.35 tons/yd³ (1.6 t/m³) | 5% |
| Decomposed granite | 1.4 tons/yd³ (1.66 t/m³) | 15% |
| Lava rock | 0.6 tons/yd³ (0.71 t/m³) | 5% |
- Mulch: Bulk wood mulch typically weighs about 400–800 lb per cubic yard depending on the wood and how wet it is. It is sold by volume, so the weight matters mainly for hauling. Bagged mulch is most often 2 ft³ (about 57 L); 1.5 and 3 ft³ bags are also common.
- Topsoil and compost: Moist, loose topsoil commonly weighs about 1–1.2 tons per cubic yard; compost is much lighter and fill dirt heavier. Moisture changes the weight a lot. Bagged topsoil is often 0.75 or 1 ft³ (about 20–28 L); garden soil and compost bags vary.
- Sand: Dry, loose sand typically weighs about 2,600–2,800 lb per cubic yard (roughly 1.3–1.4 tons); damp sand is heavier. Bagged sand is usually sold by weight, most often 50 lb (about 25 kg in metric markets).
- Landscape rock: Most decorative stone weighs about 1.3–1.5 tons per cubic yard; lava rock is far lighter. Ask your supplier for the weight of the stone you choose. Bagged decorative stone is commonly 0.5 ft³ (about 14 L); larger stone is often sold in 0.5 ft³ or by weight.
- Pavers: Common concrete and clay paver sizes. Many “4 × 8” pavers are actually metric (about 3.9 × 7.9 in); check the manufacturer’s actual size and pieces per square foot. A typical patio build-up: 4–6 in of compacted road base (more for driveways) and a 1 in screeded bed of coarse concrete sand.
- Sod: Common sod sizes: 16 × 24 in slabs (2.67 ft²), 18 × 24 in slabs (3 ft²) and 2 × 5 ft rolls (10 ft²); metric turf is commonly sold in 1 m² rolls. A pallet typically covers about 400–500 ft² (around 40–50 m²); farms vary, so check yours.
Block, brick, mortar and rebar
Unit counts use the actual (specified) size of each block or brick plus the mortar joint, so the count per square foot or meter follows from the geometry rather than a fixed table. Mortar volume is the joint volume around each unit.
- Standard concrete masonry units: US blocks are specified 3/8 in smaller than their nominal size (an 8 × 8 × 16 block is 7 5/8 × 7 5/8 × 15 5/8 in) and laid with 3/8 in joints; face shells are typically about 1 1/4 in thick. Metric blocks are common 440 × 215 mm and 390 × 190 mm sizes with 10 mm joints.
- Typical specified brick sizes: US modular 7 5/8 × 2 1/4 × 3 5/8 in, engineer modular 7 5/8 × 2 3/4 in, king 9 5/8 × 2 5/8 in and utility 11 5/8 × 3 5/8 in; UK standard 215 × 65 × 102.5 mm; Australian standard 230 × 76 × 110 mm. Brick tables based on nominal sizes give slightly lower counts (6.75 modular bricks per ft², 60 UK bricks per m²).
- Premixed mortar mix yields roughly 0.67 ft³ per 80 lb bag once mixed (about 0.52 L per kg); check your bag. Brick is assumed fully bedded; hollow block is bedded on its face shells only.
- Nominal bar weights: US sizes per ASTM A615 (#3 0.376, #4 0.668, #5 1.043, #6 1.502 lb/ft); metric bars by the standard d² ÷ 162 kg/m (10 mm 0.617, 12 mm 0.888, 16 mm 1.578 kg/m).
- Lap splices are often specified at around 40 bar diameters (20 in for #4); your plans or engineer set the actual lap.
Drywall, flooring, tile, carpet and wallpaper
- Common drywall sheets are 4 × 8, 4 × 10 and 4 × 12 ft (1200 × 2400, 2700 and 3000 mm). Typical finishing rules: about 1 screw per ft² (32 per 4 × 8 sheet), roughly 370 ft of joint tape and about 10 gallons of premixed joint compound per 1,000 ft² of drywall for a three-coat finish.
- Box coverage varies widely by product (often 15–30 ft² per box); the number printed on the box is what counts.
- Common tile sizes. Grout joints are usually 1/16–1/8 in (1.5–3 mm) for rectified tile and 1/8–3/16 in for others.
- Broadloom carpet is usually made 12 ft wide (some 13 ft 6 in or 15 ft); metric rolls are commonly 4 m or 5 m wide. Seams are placed so each room is covered with as few strips as possible.
- Typical rolls: US double rolls about 20.5 in × 33 ft (56 ft²) or 27 in × 27 ft; European rolls 0.53 × 10.05 m (5.3 m²). Pattern repeat is printed on the label.
- Cement grout weighs roughly 1.6 kg per liter (about 100 lb/ft³) once mixed and cured; bag coverage charts from grout makers are based on the same joint-volume formula.
Roofing, siding, gutters and carpentry
- A roofing square is 100 ft² (9.29 m²). Standard asphalt shingles come 3 bundles per square; synthetic underlayment rolls commonly cover 10 squares and #15 felt about 4; drip edge comes in 10 ft lengths; a bundle of hip and ridge cap covers roughly 25 linear ft.
- Typical waste: about 10% for simple gable roofs, 15% for hip roofs and roofs with valleys or dormers.
- Siding is sold by the square (100 ft²); vinyl siding boxes commonly hold 2 squares. Check the box, since profiles differ.
- Gutter sections are commonly 10 ft long (seamless gutter is formed on site); hangers every 24 in (closer in snow country); one downspout per 30–40 ft of gutter is a common guide. This is a material count, not a drainage or code sizing.
- Typical wood fence: posts every 8 ft, 2 rails up to about 4 ft high and 3 rails for taller fences, 5 1/2 in wide pickets, post holes about three times the post width and one third of the post length deep (below frost line where required).
- Typical decking: 5/4 × 6 or 2 × 6 boards (5 1/2 in face), 1/8–1/4 in gaps, joists 16 in on center (12 in for some composite boards or diagonal layouts), about 2 fasteners per board at each joist.
- Common US residential code values (IRC): maximum riser 7 3/4 in and minimum tread 10 in. Codes vary by location; your local building department decides.
- Plywood and OSB are commonly 4 × 8 ft (1220 × 2440 mm), with 4 × 9 and 4 × 10 ft sheets for tall walls; metric 1200 × 2400 mm sheets are also common.
Cost estimates
Prices are optional and always entered by you; there is no live store pricing. Cost is the purchase quantity (after rounding) times your price, so it reflects what you will actually pay for whole bags, cans or pieces. Delivery fees, tax and labor are not included.
How the calculators are tested
Every formula lives in one place in the code and is covered by automated tests. Unit conversions are checked against the published definitions above, and every calculator is tested against hand-worked examples in US and metric units, including edge cases such as exact package multiples, cut-outs larger than the area, and invalid input. The worked example on each calculator page is produced by the same code as the calculator, so the article and the tool can never disagree.
Limitations
- Real surfaces are rarely perfect rectangles or perfectly level; measure carefully and use the allowance.
- Material weights, coverage and yields vary by product, supplier, moisture and surface. Use the figure on the product when you have it.
- Results are planning estimates, not engineering, structural or code advice. Follow manufacturer instructions and local building codes.