Sources & formulas
Every calculator on GarageDoorCalcs rests on established arithmetic plus stable garage-door conventions. Unlike topics with a time dependency, "verification" here is mathematical: each formula is tested against known values and is therefore correct for good. Here are the technical foundations by area.
Identities & geometry
- Area: door area (sq ft) = width_ft × height_ft; there are 365 days in a year (spring-life identity).
- Framing clearances: rough opening = door size; minimum backroom = door height + ~18 in; side room ≈ 3.75 in each jamb; headroom ≈ 10 in (standard torsion) or ~4.5 in (low-headroom track) — labeled conventions.
Sizing conventions (labeled typicals)
- Standard US door sizes: single 8×7 / 9×7 ft; double 16×7 / 16×8 ft.
- Material weight: ~1.8 lb/sq ft (aluminum/glass) to ~3.5 lb/sq ft (solid wood) — labeled typicals.
- Opener HP: ½ HP under ~150 lb, ¾ HP ~150–350 lb, 1+ HP over ~350 lb.
- Springs: torsion vs extension; typical 10k/20k/30k-cycle ratings; life = rated cycles ÷ (cycles/day × 365).
- R-value: ~R0–6 (1-layer), R6–9 (2-layer), R9–19 (3-layer) — labeled bands, measured differently by maker.
Cost tools
- Every cost tool uses the prices you enter ($ per door, $/hr or flat labor, $/panel, $/spring, $/set, $/ft, $/sq ft) — no door, opener or labor price is stored, so the site needs no maintenance. Cost bands are a labeled sanity guide.
- Project cost: total = (door price + labor + Σ add-ons − trade-in) ×(1 + contingency).
- Insulation payback: years = added insulated cost ÷ annual energy $ saved — illustrative only.
Door, opener, material and labor prices, permit rules, local code and wind-load requirements vary by place and change over time — always get itemized written quotes from a licensed, insured garage-door installer and confirm code with your local authority. ⚠️ Garage-door springs and cables store extreme mechanical energy — spring, cable and off-track work is for a trained technician, never DIY. Hard-wired opener circuits are for a licensed electrician.