How we calculate

Every number on YardSums comes from the formulas on this page. Each formula is covered by automated tests against hand calculations, and every calculator page shows its own math for your inputs.

Rounding: once, at the end, and up

• We keep full precision through the whole calculation and round only the final purchase quantity.
• Things you buy by the piece (bags, bundles, rolls, gallons, posts, pickets) always round up to a whole unit. Running short mid-project costs more than one spare bag.
• Bulk materials round up to the step suppliers sell: ready-mix concrete to the nearest 0.25 cu yd with a 1 cu yd minimum; gravel, topsoil and mulch to the half yard or half ton.
• Bags are counted by the volume printed on the bag, never by weight, because weight changes with moisture.

Unit conversions

The metric switch on each calculator converts the sizes you type. Purchase quantities stay in the units US stores sell (80 lb bags, cubic yards, gallons), with metric equivalents where they help. When you switch units and back, we keep your exact sizes, so the rounded numbers in the fields never change the answer.

Concrete

• Volume (cu ft) = length (ft) × width (ft) × thickness (in) ÷ 12, plus the waste you choose (10% by default).
• Bag yields: 80 lb = 0.6 cu ft, 60 lb = 0.45 cu ft, 50 lb = 0.375 cu ft, 40 lb = 0.3 cu ft, from the volume printed on standard concrete mix bags.
• Gravel base under a slab: 4 in deep plus 10% for compaction, at 1.4 tons per cu yd.

Gravel

• Volume (cu ft) = length × width × depth (in) ÷ 12; cubic yards = cu ft ÷ 27.
• Weight: 1.4 tons per cu yd by default; the calculator offers pea gravel / river rock 1.4, crushed stone 1.35, heavy (#57, wet) 1.6. Real stone ranges from about 1.3 to 1.7 tons per yard depending on size, type and moisture, so ask your supplier for theirs.
• Bagged gravel: 0.5 cu ft per 50 lb bag.

Paint

• Wall area = room perimeter × wall height, minus 20 sq ft per door and 15 sq ft per window. Paint area = wall area (plus the ceiling if you include it) × coats.
• Coverage: 350 sq ft per gallon per coat (most cans say 350 to 400); primer 250 sq ft per gallon, one coat.
• We pick the cheapest mix of gallons, quarts and 5 gallon pails that covers the area, at your prices or typical ones. Pails are considered from 4 gallons up.

Mulch

• Volume (cu ft) = length × width × depth (in) ÷ 12.
• Bags: 2, 1.5, 3 cu ft sizes, counted by the volume printed on the bag. A cubic yard is 13.5 bags of 2 cu ft.
• Bulk mulch rounds up to the nearest 0.5 cu yd.

Topsoil

• Volume (cu ft) = length × width × depth (in) ÷ 12, plus any extra you choose for settling.
• Bags: 0.75 and 1 cu ft sizes. Bags labeled "40 lb" usually hold 0.75 cu ft; we count by volume.
• Weight: 1.1 tons per cu yd by default (1, 1.1, 1.3 offered); wet soil can weigh much more.

Roofing

• Roof area: entered directly, or house footprint × pitch factor, where pitch factor = √(1 + (rise ÷ 12)²). A 6/12 roof is about 1.118 times its footprint.
• Squares = roof area × (1 + waste) ÷ 100, with 10% waste for simple roofs and 15% with hips and valleys. Bundles = squares × 3, 4, 5 bundles per square (3 for most shingles; check the wrapper).
• Underlayment rolls: synthetic 10 squares per roll, #15 felt 4 squares per roll, #30 felt 2 squares per roll. No extra waste, because roll coverage already allows for laps.
• Starter strip about 105 linear ft per bundle and ridge cap about 33 linear ft per bundle by default; read your product's label.

Fence

• Sections = fence length ÷ post spacing, rounded up. Posts = sections + 1, plus one per corner and per gate.
• Rails: 2 per section up to 4 ft high, 3 per section for 5 and 6 ft fences.
• Pickets = fence length ÷ (picket width + gap), rounded up. A 1×6 picket is 5.5 in wide; privacy fences have no gap, picket fences 2.5 in.
• Post holes: 3 times the post width across (10.5 in for a 4×4, which is 3.5 in actual), one third of the fence height deep with a 2 ft minimum, and 6 in of gravel at the bottom. Dig below your frost line where codes require it.
• Concrete per post = hole volume above the gravel minus the post, ÷ 0.375 cu ft per 50 lb bag of fast-setting mix, rounded up per post.

Prices

Typical prices are approximate national ranges for each selling unit, shown with the month they were checked (currently Oct 2026). They come from public prices at large home-improvement retailers and supplier price lists. Prices vary by store, region and season, so every calculator lets you type your own price; once you do, that line shows an exact total. Prices you type are saved only on your device.

Retailer names are mentioned only to describe where prices come from. YardSums is independent and not affiliated with or endorsed by any retailer.

Found a mistake?

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