How to use this calculator
- Enter garage footprint. Length × width in feet. Common sizes: 12×20 (1-car), 20×20 (2-car), 24×24 (oversize 2-car), 24×36 (3-car).
- Enter wall height. 8 ft for cars only, 9–10 ft for SUVs and trucks, 12 ft for lifts.
- Enter slab thickness. 4" for passenger vehicles, 5–6" for trucks or workshop floors with heavy equipment.
- Read your bill of materials. Concrete (yd³ + bag count), 2×4s (studs + plates), drywall sheets, shingle bundles, insulation bags, total estimate.
Formula
Slab volume + Wall framing + Drywall + Shingles for given footprint
Worked example
A 24 × 24 × 9 ft garage with a 4-inch slab: 7.1 yd³ of concrete (~320 80-lb bags equivalent), 80 2×4s, 21 drywall sheets, 19 shingle bundles, 9 insulation bags. Estimated total in materials: ~$2,650 (slab + framing + drywall + roof + insulation).
Common project sizes
Quick reference for the most common garage material calculator use cases. Use these as a sanity check on your calculator inputs.
| Project | Dimensions | Result |
|---|---|---|
| 1-car (12 × 20 ft) | 240 ft² | ~3 yd³ slab · 56 studs · 13 sheets drywall · 8 shingle bundles |
| 2-car (20 × 20 ft) | 400 ft² | ~4.9 yd³ slab · 70 studs · 18 sheets drywall · 14 shingle bundles |
| 2-car oversize (24 × 24 ft) | 576 ft² | ~7.1 yd³ slab · 80 studs · 21 sheets drywall · 19 shingle bundles |
| 3-car (24 × 36 ft) | 864 ft² | ~10.7 yd³ slab · 100 studs · 28 sheets drywall · 29 shingle bundles |
2026 cost reference
Typical retail price range in the United States for garage material. Local pricing varies by region, supplier, and grade — confirm with two or three quotes before ordering.
Per square foot (turnkey detached)
$45 – $120
$45–$60/ft² for a basic 2-car detached. $70–$100/ft² for finished interior, drywall, electrical. $100+/ft² for matched architecture, custom doors, climate control. Add $5,000–$10,000 for utility connection runs.
How we calculate this
Assumptions baked in
A turnkey estimate for a basic stick-frame detached garage: slab thickness × floor area = concrete; perimeter × 0.75 (≈ studs at 16" o.c.) + plates = lumber; perimeter × height ÷ 32 = drywall sheets; floor area × slope multiplier (1.118 for 6:12) ÷ 100 × 3 = shingle bundles; perimeter × height ÷ 88 = R-13 insulation bags. Cost figures are mid-range retail.
Accuracy and margin of error
±15% on a quick estimate basis. The biggest uncontrolled factor is the slab — uneven sub-grade and short-load fees push the concrete cost up sharply for small garages. The lumber figure is for stick-built construction; pre-engineered steel garages have a very different bill of materials.
Edge cases this calculator does not handle
For attached garages, the calculator does not size the structural connection to the house (ledger, sheathing, electrical sub-panel from the main). For garages over 1,000 ft², a permit will require a stamped foundation plan and likely truss engineering. Door and window allowances are NOT subtracted — for a typical 9×7 ft sectional door and a 3×4 ft window, manually reduce drywall by ~80 ft² and lumber by 4 studs.
Cited sources for this page
The figures and rules above are anchored to the following normative references. We link the underlying claim to its standard — not as generic SEO trust signals, but so you can audit any number on this page against a primary source.
Attached garage fire separation: 1/2" gypsum on garage side of common wall, 5/8" Type X if there is a habitable room above the garage, per IRC R302.6.
Source: IRC 2021 Section R302.6 — Dwelling-garage fire separation
Tips for accurate results
- Always permit. A 2-car detached garage triggers building permit + setback inspections in nearly every U.S. jurisdiction.
- Don't skimp on the slab. A 4" slab works for cars; trucks and any lift application need 5–6" with welded wire reinforcement.
- Roof pitch on garages is typically 4/12 to 6/12. Lower pitches need ice-and-water shield in snow zones.
- Add a full vapor barrier under the slab — a garage floor without one will sweat and ruin paint, drywall, and stored items.
When to consult a pro
Garage builds are above the DIY threshold for nearly all homeowners — the framing, roof, and electrical exceed what most weekend warriors safely handle. Hire a general contractor or use a prefab kit (Tuff Shed, Mighty Mule) where the structure ships pre-engineered. DIY components: interior finish, paint, garage door opener, shelving — these are fine for owners.