Concrete Calculator
Volume + bag count + delivery decision tool for deck footings (cylindrical sonotube, square forms, bell-bottom flared base) and slabs (floating-deck pads, walkway sections). Enter pour geometry + footing count + depth + waste factor; pick brand (Quikrete / Sakrete / generic), bag size (60lb / 80lb), and mix strength (3000-4500 psi). Returns total volume (cubic yards + cu ft + gallons), bag counts, ready-mix delivered cost (regional $/yd + short-load surcharge if <3 yd), and bags-vs-delivery recommendation tuned to your pour. IRC R507.3.1.2 rebar spec auto-flagged for footings ≥12″ Ø. Pairs with Footing Depth Calculator (depth + diameter sizing) and Frost Depth Calculator (regional lookups).
How much concrete do I need for deck footings?
- 1 footing (12×48)
- 0.31 cu ft
- 80-lb bag yield
- 0.60 cu ft
- Ready-mix $/yd
- $165–$290
Inputs
Pour shape
Footing geometry
Mix + bag
Results
cylindrical · 4000 psi · Quikrete · PA (Northeast, $263/yd avg delivered)
Under 1 cu yd — bags win on price (avoid $125 short-load fee). 31 bags × $7.25 = $225 vs delivered $388.
Mix strength: 4000 psi
IRC R507.3 · ACI 318-19Meets IRC + ACI 318-19 deck-footing minimum (4000 psi). Premium 4500 psi recommended for freeze-thaw regions or high-load applications.
Rebar REQUIRED — footing 12″ Ø exceeds 12″ threshold
IRC R507.3.1.22 × #4 (1/2″ Ø) rebar verticals + 3 × #4 horizontal hoops at 12″ o.c. per IRC R507.3.1.2. Tie hoops to verticals with 16-ga steel tie wire. Provide 3″ concrete cover from edge of footing.
Volume: 18.14 cu ft = 0.67 cu yd = 135.7 gal
ASTM C387 / C94 measurementRaw 16.49 cu ft + 10% waste = 18.14 cu ft total. Per-footing volume 2.75 cu ft × 6 footings.
Bag count: 41 × 60lb OR 31 × 80lb
ASTM C387 packaged concreteQuikrete pre-mix yields: 60lb = 0.45 cu ft, 80lb = 0.60 cu ft (per ASTM C387). Preferred 80lb count: 31 bags @ $7.25 each.
Cost comparison — bags vs delivered
Bag option includes pre-mix material only — add mixer rental ($60-90/day for >5 bags), water hose, and 4-8 hours of mixing time for 30+ bag pours. Delivered option includes pre-mixed concrete + truck delivery + on-site pour (truck operator does the dispensing; you handle finishing). Both prices reflect 2026-Q1 retail; verify with local supplier before pouring.
Volume + math breakdown
- Per-footing volume
- 2.75 cu ft
- × 6 footings
- 16.49 cu ft
- + 10% waste
- 18.14 cu ft
- Total cubic yards
- 0.67 yd³
- 60lb bags needed
- 41 bags
- 80lb bags needed
- 31 bags
- Ready-mix billed yards (rounded to 0.25)
- 1 yd³
Cylindrical volume = π × (Ø/2)² × depth ÷ 1728 (cu ft). Bag yields per ASTM C387: 60lb = 0.45 cu ft, 80lb = 0.60 cu ft.
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How to use
How to use the concrete calculator in 5 steps.
- 1
Pick pour shape
Cylindrical (sonotube — most common for deck footings) / Square (formed footings, less common) / Bell-bottom (flared base for higher load — IRC R507.3.1.1 allowance) / Slab (floating deck pad, walkway, BBQ pad). Each shape exposes the relevant geometry inputs (diameter + depth for cylindrical, side + depth for square, etc).
- 2
Enter geometry + count
Footings: count (typical residential deck has 4-8 footings depending on size + post spacing) × diameter (8″ for light loads, 12″ standard, 16-24″ for high load) × depth (frost depth + 6″ — use the Frost Depth Calculator). Slab: length × width × thickness (4″ min for walking surfaces, 6″+ for vehicle loads). Bell-bottom: cylinder Ø at top, bell Ø at base, bell-flare height.
- 3
Waste factor + mix strength
Waste factor 5-15% (default 10%) — covers spillage, batch under-yield, frost-lens correction. Use 10-12% for typical pours, 15% for cold weather or complex pours. Mix strength: 3000 psi (driveway/sidewalk), 3500 psi (general residential), 4000 psi (IRC + ACI 318 minimum for deck footings + slabs), 4500 psi (heavy load, freeze-thaw zones, premium spec).
- 4
Brand + bag size
Quikrete + Sakrete are the major national brands — same yield (60lb = 0.45 cu ft, 80lb = 0.60 cu ft), ~3-5% price difference. Generic / yard-brand is 10% cheaper but check ASTM C150 compliance on the bag. Bag size: 60lb is easier to lift (good for smaller pours, older DIYers); 80lb requires fewer bags for the same volume. Most contractors use 80lb.
- 5
Read the recommendation
The calc returns bags-or-delivered guidance based on total volume. Under 0.5 cu yd → bags always. 0.5-3 cu yd → math-driven (bags vs delivered cost + convenience). 3+ cu yd → ready-mix wins. Short-load surcharge ($75-175) applies to ready-mix orders <3 cu yd. Cost breakdown shows bag price × count vs delivered $/yd × yards + short-load fee.
How we calculate
How DeckMath calculates this — IRC 2021 sources.
The Concrete Calculator is the volume + bag + delivery decision tool for deck footings (cylindrical sonotube, square forms, bell-bottom flared base) and slabs (floating-deck pads, walkway sections). Enter pour geometry, footing count, depth, and waste factor; pick brand (Quikrete / Sakrete / generic) + bag size (60lb / 80lb) + mix strength (3000-4500 psi). Returns total volume (cubic yards + cu ft + gallons), 60lb & 80lb bag count, ready-mix delivery cost (regional $/yd + short-load surcharge if <3 yd), and a bags-vs-delivery recommendation tuned to your scope. IRC R507.3.1.2 rebar spec auto-flagged for footings ≥12″ Ø. 2026-Q1 retail bag + ready-mix pricing.
IRC references
- IRC 2021 R507.3 — Deck footings (depth, diameter, bearing capacity)
- IRC 2021 R507.3.1.1 — Permitted footing types (cylindrical, bell-bottom, spread, helical pile)
- IRC 2021 R507.3.1.2 — Rebar required for footings ≥12″ diameter (2 verticals + 3 hoops minimum)
- ACI 318-19 — Building Code Requirements for Structural Concrete (4000 psi min for residential decks)
- ASTM C150 — Standard Specification for Portland Cement (verify packaged mix compliance)
- ASTM C387 — Standard Specification for Packaged Dry Combined Materials (60lb/80lb bag yield)
- ASTM C94 — Standard Specification for Ready-Mixed Concrete (delivered mix requirements)
Verify against the published source: 2021 International Residential Code (ICC).
2026-Q1 retail at Home Depot/Lowes/local supply. Quikrete: $5.95/60lb · $7.25/80lb (yields 0.45 / 0.60 cu ft). Sakrete: $5.75/60lb · $7.00/80lb (same yield). Generic yard-brand ~$5.25/60lb · $6.50/80lb. Ready-mix delivered $/yd (2026-Q1 regional averages): Northeast $220-270, West $230-290, South $165-215, Southeast $175-220, Midwest $195-245. Mix strength premium: +$8/yd for 3500 psi, +$18 for 4000, +$32 for 4500. Short-load surcharge $75-175 for orders <3 cu yd. Truck minimum 1 yd. Conversions: 1 cu yd = 27 cu ft = 202 gal; 60lb bag = 0.45 cu ft; 80lb bag = 0.60 cu ft (ASTM C387).
Standard sonotube footing. Diameter ÷ 2 = radius (inches), times depth (inches), times π, divided by 1728 (cu in per cu ft). Example: 12″ Ø × 42″ deep = π × 6² × 42 ÷ 1728 = 2.75 cu ft per footing. Six 12″ × 42″ footings = 16.5 cu ft = 0.61 cu yd raw + 10% waste = 0.67 cu yd.
Cylinder body + truncated cone (frustum) flare at base. Frustum: V = π × h × (R² + R×r + r²) ÷ 3, where R = bottom radius, r = top radius. Bell-bottoms transfer load to a wider footprint — IRC R507.3.1.1 allows them for higher-load applications without requiring full-diameter sonotube the full depth.
Standard yields per ASTM C387 (packaged concrete mix): 60lb bag = 0.45 cu ft, 80lb bag = 0.60 cu ft. Always round up — partial bags don't help. Per cubic yard (27 cu ft): 60 × 60lb bags OR 45 × 80lb bags. A typical 6-footing residential deck pour = 18-25 × 80lb bags.
Billed yards round up to nearest 0.25 yd. Plant minimum 1 yd. Mix strength premium: +$8/yd for 3500, +$18/yd for 4000, +$32/yd for 4500. Regional $/yd: Northeast/West ~$240-280, Midwest ~$210, South ~$185. Short-load fee $75-175 for orders <3 yd (covers truck round-trip + idle time). At 3+ yd, no surcharge.
Under 1 yd, bag cost (~$130-180) always beats delivered ($165 + $125 short-load = $290 typical). 1-3 yd: do the math — bags around $200-540, delivered $300-740. 3+ yd: 60+ bags is 4-8 hr of manual mixing vs 20-min truck pour. Convenience + batch consistency tip toward delivery beyond 3 yd regardless of pure cost.
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People also ask
Concrete questions, answered.
45 × 80lb bags = 1 cubic yard (27 cu ft). Each 80lb bag yields 0.60 cu ft, so 27 ÷ 0.60 = 45. For reference: 60 × 60lb bags = 1 cu yd (each 60lb bag = 0.45 cu ft). At 2026-Q1 retail: 45 × 80lb Quikrete @ $7.25 = $326 vs 60 × 60lb @ $5.95 = $357. 80lb is the better $/cu yd value, but heavier to lift. Generic/yard-brand is ~10% cheaper across both sizes.
Per footing: π × (diameter/2)² × depth ÷ 1728 = cubic feet. A 12″ diameter × 42″ deep footing: π × 6² × 42 ÷ 1728 = 2.75 cu ft. Multiply by footing count, then add 10% waste. Example 6-footing residential deck: 6 × 2.75 × 1.10 = 18.15 cu ft = 0.67 cu yd. That's 31 × 80lb bags or a 1-yd ready-mix delivery (with $75-175 short-load surcharge). Most 14×16 ft decks need 4-6 footings; 16×20 ft decks 6-8 footings.
Under 1 cubic yard (typical 4-footing small deck): bags always — short-load surcharge nearly doubles delivered cost. 1-3 cubic yards (6-8 footing typical deck): math-driven, often bags by 15-25%. 3+ cubic yards (large deck or slab pour): ready-mix wins decisively — 60+ bags is 4-8 hours of manual mixing vs a 20-min truck pour. Real-world: most residential deck footing pours (4-8 footings) end up in the 'bags win' zone because of the short-load fee.
4000 psi minimum per IRC + ACI 318 for residential deck footings. Lower strengths (3000-3500 psi) are technically allowed by some legacy codes but most modern jurisdictions require 4000 psi for any structural footing carrying vertical load. 4500 psi is upgrade-spec for: freeze-thaw zones (NJ/NY/PA/OH/MI northern), high-load decks (hot tubs, kitchens), or coastal/marine exposure. Quikrete + Sakrete sell pre-mixed 4000 psi (red bag); 3000 psi (yellow bag) is sidewalk/driveway grade only.
$165-290/cu yd national average, regionally adjusted. Northeast/West $230-290 (CA + NY most expensive). Midwest $195-245. South/Southeast $165-220. Mix-strength upcharge: +$8/yd for 3500 psi, +$18/yd for 4000 psi, +$32/yd for 4500 psi. Short-load surcharge: $75-175 flat fee for orders <3 cu yd (covers truck trip cost when not running full). Most plants have a 1-yard minimum order. For a 4000-psi 1-cu-yd order in PA: ~$240/yd × 1 + $125 short-load fee = ~$365 delivered.
Below the local frost line + 6 inches, minimum 12″ deep per IRC R403.1.4 + R507.3. Frost depths vary by region: Florida/southern Texas 0″ (can use 12″ minimum); Tennessee/Virginia 18-24″; PA/Ohio/NY 36-42″; Minnesota/Maine/Wisconsin 48-60″; Anchorage AK 100″ (permafrost zone). Use the Frost Depth Calculator for your exact location. Footing bottom must rest on undisturbed soil with bearing capacity ≥1,500 psf (clay) or ≥3,000 psf (sandy/silty) per IRC Table R401.4.1.
Initial set: 4-8 hours (cannot be disturbed). Walkable: 24-48 hours. Full structural strength: 28 days (ACI 318 standard). Critical milestones for deck builders: 1) Don't touch fresh concrete for 4-8 hours after pour. 2) Don't load posts onto wet footings for 48 hours minimum. 3) Don't apply full deck weight until day 7 (~65% strength). 4) Avoid freezing temperatures for 7 days minimum — frost damages crystalline structure. Hot weather: keep moist with damp burlap or curing compound for 7 days. Cold weather: insulate or use accelerator-mix products like Quikrete High-Strength.
IRC R507.3.1.2 requires rebar for footings ≥12″ diameter. Spec: 2 × #4 (1/2″ Ø) vertical rebar + 3 × #4 horizontal hoops at 12″ on-center. Tie hoops to verticals with 16-gauge steel tie wire. Provide 3″ concrete cover from edge of footing. Smaller footings (<12″ Ø) don't require rebar by code, but local jurisdictions sometimes require it anyway — check local building department. Cost: $8-15 per footing for #4 rebar + ties. Add to materials BoM.
Functionally identical for most home-use applications. Both are pre-blended Portland cement + sand + aggregate meeting ASTM C387. Same bag yields: 60lb = 0.45 cu ft, 80lb = 0.60 cu ft. Same workability. Pricing: Quikrete ~3-5% premium at most retailers due to broader distribution. Sakrete more common in southeast/east coast Home Depots; Quikrete dominates west + national Lowes. For deck footings, either works equally well at 4000 psi. Generic yard-brand pre-mix is 10% cheaper than both — verify ASTM C150 compliance on the bag.
Under 5 bags: mix in a wheelbarrow with a flat hoe (~5-10 min per bag, hard work). 5-30 bags: rent a portable concrete mixer ($60-90/day at Home Depot/United Rentals). 30+ bags: rent + budget 4-8 hours mixing time, OR get ready-mix delivered. Manual mixing risks batch inconsistency (different water ratios across batches → different cure strength) — for structural footings, this matters. Most pros use a mixer or ready-mix for any pour >10 bags. Add water at 1 gal per 60lb bag or 1.25 gal per 80lb bag — never exceed (weakens concrete).
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