How to read this page
Every figure below is a value the calculator actually uses, not a general recommendation. Where a manufacturer publishes a range, the site takes the conservative end so an order is more likely to be enough. Your site, your product, and your substrate can all move the real number, so treat these as planning values and adjust with what you measure.
The page exists so that a result is never a black box. If a calculator says four bags, one of the rows below explains the yield behind that count, and the worked example on the calculator page shows the arithmetic in full.
Assumptions used by each calculator
| Tool | Assumption | Value | Basis |
|---|---|---|---|
| Paint | Interior latex coverage | 350 sq ft per gallon | Conservative end of the 350–400 sq ft range published on premium interior paint data sheets. |
| Paint | Primer coverage | 200 sq ft per gallon | Primer technical data sheets; primer soaks into bare substrate. |
| Paint | Door / window deduction | 21 / 15 sq ft | Standard 3×7 ft door and 3×5 ft window openings. |
| Mulch | Bag volumes | 2 and 3 cu ft | Common retail bag sizes; bulk is sold by cubic yard. |
| Concrete | 80 lb bag yield | 0.6 cu ft | Manufacturer-published yield for 80 lb concrete mix. |
| Concrete | Waste factor | 10% | Allowance for uneven subgrade and spillage. |
| Tile | Cut waste | 10% straight / 15% diagonal | Layout-dependent cutting allowance. |
| Tile | Grout | 8–12 lb per 100 sq ft | Industry rule of thumb; smaller tiles need more grout. |
| Deck | Board gap | 1/8 in | Drainage and seasonal movement allowance. |
| Deck | Joist count | 16 in O.C. + 1 | Common residential framing spacing. |
| Gravel | Bulk density | 1.35–1.50 tons per cu yd | Material-dependent range; moisture and source change the number. |
Source list
These are the publishers the site relies on. Each link goes to the publisher's site rather than a specific document, because product literature moves; the assumption table names the figure that comes from each source.
- BehrInterior paint coverage and surface preparation.
- Sherwin-WilliamsPaint and primer technical data sheets.
- QuikreteBagged concrete and aggregate yields.
- Tile Council of North AmericaTile installation and grout guidance.
- American Wood CouncilSpan tables and framing guidance.
- ASTM InternationalUnit definitions and material standards.
What we do not model
The calculators are quantity tools, so several real project costs and constraints sit outside them:
- Regional material pricing, delivery minimums, sales tax, and labor.
- Structural design, reinforcement, and permit requirements.
- Site access, truck reach, and the weight limit of a delivery load.
- Product-specific installation rules that override a general coverage figure.
Those are the questions a supplier, a local building department, or a licensed professional should answer.
Review date
These assumptions were last reviewed on . The editorial standards page explains how corrections are handled, and the about page covers who writes the site.