Every number on Tupep comes from somewhere. This page explains where.
The three-step process
1. Find the formula the trade uses. Not a simplified version, but the actual geometry or coverage relationship contractors and estimators work from. For epoxy that is the 1,604 square feet per gallon at one mil constant, which is pure unit conversion from a gallon’s volume. For drywall it is surface area divided by sheet area. For concrete it is cubic volume converted to yards and then to bag counts.
2. Cross-check the constants. Coverage figures differ between manufacturers, sometimes by 15 to 20 percent for what is nominally the same product. Where published figures diverge, we compare multiple technical data sheets and use the conservative number, the one that leaves you with a little extra rather than a little short. Running out mid-project costs more than a returned bag.
3. Choose a defensible waste factor. Waste is not padding. It is the material genuinely lost to cuts, corners, openings, breakage, and offcuts that fit nowhere else. A straight-lay tile floor wastes less than a diagonal one, and a room full of windows wastes more drywall than a blank wall. We set each factor to the layout it describes, and we state it on the page.
Where our figures come from
We work from primary sources wherever one exists:
- Manufacturer technical data sheets, for coverage rates on paint, epoxy, joint compound, adhesives, and sealers
- Trade association and industry handbooks, for assembly standards in drywall, tile, and concrete work
- Model building codes, for stair geometry, fire-rated assemblies, and insulation minimums
- University extension services and agricultural agencies, for seeding rates and sod coverage, which vary by grass species and region
- Product packaging specifications, for bag yields, box coverage, roll lengths, and piece counts
We do not source figures from other calculator sites. Where a number is widely repeated online without a traceable origin, we either trace it back to a primary source or we do not use it.
What our calculators assume
| Assumption | Default | Why it matters |
|---|---|---|
| Stud and joist spacing | 16 inches on center | Drives screw counts and sheet layout |
| Ceiling height | 8 feet unless entered | Drives wall surface area |
| Waste factor | 5 to 15 percent by material and layout | Diagonal, patterned, and large-format work waste more |
| Rounding | Always up, to purchasable units | You cannot buy 6.3 bags |
| Substrate condition | Sound and prepared | Porous or damaged surfaces absorb more material |
What we deliberately do not calculate
Structural members. Beam spans, header sizing, footing dimensions, and load paths are engineering calculations. Getting them wrong is a safety issue, not an inconvenience. We do not offer them.
Electrical and gas work. Wire sizing, circuit loads, and gas line sizing are code-governed and jurisdiction-specific. Use a licensed trade.
Anything requiring inspection sign-off. Our estimates help you buy materials. They are not a substitute for a permit set or an inspector’s approval.
Accuracy, limits, and corrections
Our calculators are planning tools. Real projects have irregular walls, out-of-square corners, and substrates that behave differently than the spec sheet promised. Treat every result as a starting quantity and verify it against your own conditions.
If you find an error, whether a wrong constant, a waste factor that does not match your experience, or a formula that breaks in an edge case, email info@tupep.com. Corrections are published along with the calculator’s updated date.