Material math, done properly
Free quantity and cost estimators for contractors, tradespeople and serious DIYers. Enter your dimensions, get exact quantities, bag counts, waste allowance and a total — plus a printable materials list to take to the supply yard.
Concrete slab takeoff
What makes these different
- An adjustable waste factor Most calculators hardcode it or leave it out. Every tool here puts it on a slider with a sensible default and tells you when your setting is optimistic.
- Whole purchasable units Bags, boxes, bundles and sheets rounded up to what you can actually buy — not a raw volume you have to convert at the counter.
- Cost, not just quantity Enter your unit prices and get a line-itemised total. Compare bag sizes, ready-mix against bagged, or rebar against mesh.
- A printable materials list Copy it, download a CSV, or print a clean one-page takeoff sheet with the assumptions and the sources on it.
- Imperial and metric One toggle switches every input and every result. Values convert exactly and round-trip without drift.
- Every figure sourced and dated Bag yields, coverage rates and code limits all cite where they came from and when they were last checked.
All 14 calculators
Structure
Interior
Outdoor
Systems
How much material do I need?
Nearly every material estimate reduces to the same four steps, and the errors happen in the same four places every time.
- Measure the geometry. Area for coverings, volume for fill, length for linear material. Convert everything to one unit first — mixing feet and inches in a single multiplication is the most common arithmetic error there is.
- Add a waste allowance. Ten percent is the usual starting point. It goes up for diagonal layouts, cut-up rooms, uneven subgrade and anything you are culling for defects. It is not padding — it is the material that ends up in the offcut pile.
- Divide by the coverage of the unit you are buying. This is where the published figures matter: an 80 lb bag of concrete yields 0.60 ft³, a gallon of paint covers about 350 ft², a bundle of shingles covers a third of a square.
- Round up to whole units. You cannot buy 7.4 boxes of flooring. Rounding up is not optional and it is why what you buy is always meaningfully more than the size of the room.
Where estimates usually go wrong
The same seven mistakes account for most of the "why did I run short" calls. Each one is handled explicitly by the calculator linked below it.
- 01Using nominal lumber sizes as actual
A 2×4 is really 1.5″ × 3.5″; a 1×6 is 5.5″ wide.
6–9% short Use actual dimensions for takeoff, not nominal. → - 02Forgetting the roof overhang
Roof area is not the same as building footprint.
10–15% short Measure true roof area, eaves included. → - 03Ignoring the pitch multiplier
A 6:12 roof is 11.8% larger than its footprint.
12–41% short Apply the pitch multiplier to the footprint area. → - 04Not subtracting the post from a post hole
A 4×4 fills 13% of a 12″ hole, a 6×6 nearly 30%.
13–30% over Subtract the post size in post-hole mode. → - 05Missing the "plus one" on bar spacing
A 20 ft span at 12″ spacing takes 21 bars, not 20.
1 short, each way Let the bar-spacing arithmetic run itself. → - 06Ordering loose volume for a compacted depth
Compactable aggregate settles about 20% once placed.
20% short Add 15–25% for loose-to-compacted settlement. → - 07Measuring stair rise to the subfloor
Rise is finished floor to finished floor, not framing.
Fails inspection Measure finished-to-finished, every time. →
Every one of those is handled explicitly by the calculator it applies to, and each tool page writes out the formula, the assumptions and a fully worked example with real numbers so you can check the arithmetic yourself.
Imperial or metric
Every tool has a unit toggle. Switching it converts your inputs exactly — 12 ft becomes 3.658 m and back again with no drift — and swaps the product catalogue to match: 80 lb bags become 25 kg bags, gallons become litres.
What the toggle deliberately does not do is change currency or country. Construction materials are not convertible the way currencies are: US construction uses shingles, 2×4s and 80 lb bags, while other markets use entirely different products at entirely different sizes. A currency toggle on a roofing calculator would produce confidently wrong answers, so these tools stay US-market and give you the unit system you prefer to work in.
About the figures
Every rate, coverage figure and code limit used across these tools comes from a published source, and each one carries the date it was last checked. Bag yields come from manufacturer data sheets. Coverage rates come from technical data sheets. Code limits cite the section they come from — IRC 2021 for stairs, IECC 2021 for insulation R-values, ACI 318 for concrete cover.
Where a figure is a convention rather than a standard, it says so. Where adoption varies — energy code in particular lags by state, sometimes by more than a decade — the tool says that too, because the number a national table gives you is not necessarily the number your inspector will use.
MaterialMath is an independent, third-party reference tool — not affiliated with, endorsed by, or operated on behalf of any manufacturer, retailer or code authority named on this site. These are researched estimates for planning and budgeting, not a final verdict, and not a substitute for a professional takeoff, an engineered design, or the building code as adopted in your jurisdiction. Read the full disclaimer.