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BuildMath

BuildMath

Editorial Guidelines

How we build, source, review and correct every calculator and chart on BuildMath.

Last updated:

Our standard

A BuildMath result should match what an experienced estimator would get by hand. Every page shows the formula it uses, the assumptions behind it (waste factor, bag yield, density, code limit) and where those assumptions come from.

How calculations are produced

  1. One formula, one source of truth. Each formula is written once in code and shared by the interactive calculator and the pre-calculated tables, so the static answer and the live answer always agree.
  2. Pre-calculated pages. Size and preset pages (for example a 20x20 slab or a 6/12 roof) are generated programmatically from the same formulas; their tables, quick answers and FAQ figures are computed, not typed by hand.
  3. US units first. Feet, inches and fractions to 1/16" (or 1/32"), cubic yards, square feet, board feet, pounds and tons.
  4. Round the way the trade does. Bags, sheets, studs and sticks always round up; ready-mix rounds up to the next ¼ yd³.
  5. Waste is explicit. Material calculators offer 0%, 5%, 10% or 15% waste, and pre-calculated tables state which value they use.

Reference standards

SourceUsed for
2024 International Residential Code (IRC)Stair risers & treads (R311.7.5), wall stud size & spacing (R602.3), rafter framing and span tables (R802), roof covering slopes (R905)
ACI 332 / ACI 302.1RResidential concrete and slab-on-ground practice: thickness, base, control-joint spacing
ASTM A615Deformed steel rebar sizes and weights (#3 = 0.376 lb/ft, #4 = 0.668 lb/ft)
ASTM C33 / C387Concrete aggregates and packaged dry concrete mixes
Manufacturer data (Quikrete, Sakrete)Bag yields: 80 lb ≈ 0.60 cu ft, 60 lb ≈ 0.45 cu ft, 40 lb ≈ 0.30 cu ft
American Softwood Lumber Standard (PS 20)Nominal vs. actual dressed lumber sizes
Gypsum Association / manufacturer handbooksDrywall sheet sizes, fastening and finishing estimates

Code requirements vary by jurisdiction and by which IRC edition your area has adopted. Our pages cite the model code as a reference point; your local building department has the final word.

Review process

  • New calculators are checked against hand calculations for several inputs, including edge cases (very small, very large and fractional values).
  • Reference values (yields, densities, code limits) are re-checked when a new IRC edition is published or a manufacturer changes product data.
  • Typical prices are labeled as rough US averages and are never presented as quotes.

Corrections policy

If you find an error, email [email protected] with the page URL, your inputs and the source for the expected value. Confirmed errors are corrected promptly, and the page's review date is updated.

Advertising independence

BuildMath is funded by display advertising. Ads are clearly labeled "Advertisement" and kept separate from calculator results. Advertisers and affiliates have no input into formulas, results, tips or recommendations.

Limits of our content

Calculators produce estimates for planning and ordering. They do not replace a permit review, a site-specific engineered design or the judgment of a licensed professional. See our Terms of Service.