Methodology
The same rules apply across every calculator on DeckCalc, so a result on one page means the same thing as a result on another.
Units
Every calculator converts your input to a single internal unit — inches for lengths, square inches for areas — does the math at full precision, and converts back to your chosen display unit only at the end. Conversion never happens in the middle of a calculation, so switching units doesn't change your result beyond normal rounding.
Rounding
Purchase quantities — boards, boxes, gallons — round up, because you can't buy a partial one. Intermediate values are kept at full precision and never rounded early. Money is shown to two decimal places. Display rounding never feeds back into a calculation.
Waste
Waste is applied exactly once, at one specific step: after the base quantity is known and before the purchase quantity is rounded up. If a number you enter already has waste built in — like a board count copied from another calculator — later steps treat it as final and never add waste again.
Shared calculation engines
When two calculators rely on the same underlying math — board-layout geometry, for instance — they call the same tested function rather than each having their own copy. That keeps results consistent and means a fix or improvement only has to happen once.
Geometry and quantity vs. structural requirements
These calculators answer “how many” and “how big,” not “is this safe to build.” Joist counts, post counts, and railing layouts are quantity and spacing estimates only. Nothing here calculates allowable spans, load capacities, or code-approved dimensions — those depend on lumber species, grade, local code, and site conditions that only a verified reference or a qualified professional can confirm.
User-entered assumptions
Prices, coverage rates, and spacing choices come from you, not from an assumed database. Default values in each field are editable examples meant to show the calculator working, not universal recommendations — always double-check them against your own project and your product's label.
Why some calculations are intentionally left out
Structural calculators — joist span, beam span, footing size — aren't here yet because doing them responsibly means citing a specific, current reference standard for species, grade, size, spacing, and load. Guessing at those numbers would be worse than not offering them at all, so they wait until that reference data is deliberately built in and tested.