About Quantity Estimator
Quantity Estimator provides free, formula-based material estimators for contractors, builders, and DIYers. Every calculator uses published industry standards — not guesswork — so your material orders are accurate the first time.
What We Build
We publish targeted construction estimating calculators covering concrete, lumber, roofing, flooring, paint, electrical, HVAC, masonry, landscaping, framing, fencing, decking, drywall, and specialty applications. Each calculator:
- Uses the industry-standard formula for that material type
- Applies the correct waste factor (typically 10%)
- Shows both quantity and cost estimate
- Links to the right product at Home Depot and Lowe's
- Saves your inputs to the URL so you can bookmark or share
Formula Sources
Our calculators are built from published standards — not estimates or "rules of thumb" sourced from forum posts. The table below documents the primary source for each category.
| Category | Standard / Source | Notes |
|---|---|---|
| Concrete | ACI 318 (Building Code Requirements for Structural Concrete) | Bag coverage from Quikrete published specs (0.45 cu ft / 60lb bag, 0.60 cu ft / 80lb bag) |
| Lumber & Framing | American Wood Council (AWC) span tables | Standard 16" OC framing; board feet formula: (thickness × width × length) / 12 |
| Roofing | National Roofing Contractors Association (NRCA) guidelines | 3 bundles per square for 3-tab; 4 bundles for architectural. 10% waste built in. |
| Paint | Manufacturer coverage rates | ~350 sq ft/gal flat, ~400 sq ft/gal semi-gloss on smooth drywall. Adjusted for texture. |
| Electrical | NEC Table 310.15(B)(16) and the 3% voltage drop rule | Wire gauge upsized when calculated voltage drop exceeds 3% on the branch circuit. |
| HVAC | ACCA Manual J (simplified multiplier chain) | 20 BTU/sq ft base load adjusted for climate, ceiling height, windows, and insulation. |
| Insulation | DOE recommended R-values by climate zone | Zones 1–8 per DOE Building Technologies Office guidelines. |
Accuracy & Limitations
Important: These calculators provide estimates for material planning purposes. They are not a substitute for professional engineering, architectural review, or on-site measurement. Always verify quantities with your supplier before placing a large order.
Construction estimates depend on field conditions our calculators cannot know: subgrade conditions, existing structure dimensions, local code variations, and product-specific coverage rates. We recommend:
- Adding 10% to all material quantities as a waste buffer
- Confirming bag or unit coverage with your specific product's spec sheet
- Having a licensed engineer review structural calculations (headers, beams, footings)
- Checking local building codes before starting any permitted work
Affiliate Disclosure
Some links on this site are affiliate links to Home Depot, Lowe's, and Amazon. When you click through and make a purchase, we may earn a small commission at no extra cost to you. This helps support the site and keeps all calculators free. We only link to products that are directly relevant to each calculator's results.
Contact & Feedback
Found a formula error? Have a calculator you'd like to see built? We take accuracy seriously and want to know when something is wrong.
Email us at hello@constructcalc.com