DeckMath
footings + slabs · bags vs delivered · IRC R507.3

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).

Start calculating
Get 2–3 free quotes
4 shapes3000-4500 psi60lb + 80lb bag countBags vs deliveredIRC R507.3.1.2 rebar2026 regional pricingFree forever
cyd/cuft/gal·Volume conversions
60 + 45·Bags per yd³ (60lb / 80lb)
$165-290·Delivered $/yd range
3 yd threshold·Short-load fee triggers
Quick answer

How much concrete do I need for deck footings?

A standard 12"-diameter × 48"-deep deck footing needs 0.31 cu ft of concrete — about one 80-lb bag (yields 0.60 cu ft) or two 60-lb bags. A 6-footing deck typically uses 6–8 bags total. For ready-mix delivered, expect $165–$290 per cubic yard plus a $75–$175 short-load fee under 3 yd.
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

ea

in

in

Per footing2.75 cu ft

Mix + bag

%

Results

cylindrical · 4000 psi · Quikrete · PA (Northeast, $263/yd avg delivered)

Total volume
18.14 cu ft · 135.7 gal
60lb bags
Quikrete · $5.95/bag
80lb bags
Quikrete · $7.25/bag
Recommendation
short-load fee applies
Recommendation
Buy 31 × 80lb bags

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 318-19

Meets 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 R507.3.1.2

2 × #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 measurement

Raw 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 concrete

Quikrete 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

Bags (Quikrete 80lb)
$207 – $243
31 bags × $7.25/bag
Add ~$60-90/day mixer rental if >5 bags
Ready-mix delivered
$313 – $463
$263/yd avg in Northeast
+ $75-175 short-load fee (under 3 yd)

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.

How to use

How to use the concrete calculator in 5 steps.

  1. 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. 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. 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. 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. 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)

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).

Cylindrical footing volume
V = π × r² × h ÷ 1728 (cu ft)

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.

Bell-bottom volume
V = cylinderVol(topDia, height − bellHeight) + frustumVol(topDia, bellDia, bellHeight)

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.

Bag count from cubic feet
bags60lb = ceil(totalCuFt ÷ 0.45); bags80lb = ceil(totalCuFt ÷ 0.60)

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.

Ready-mix cost
delivered = max(1, ceil(yards × 4)/4) × ($/yd + mix premium) + (yards < 3 ? short-load fee : 0)

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.

Bags-vs-delivery crossover
if totalYd < 1: bags wins; if 1-3: cost comparison; if 3+: ready-mix wins

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.

Save your plan

Don’t lose this estimate.

Your inputs are preserved in the URL — email it to yourself or copy the link so you can compare with contractor bids later. No account needed.

Get matched

Want 2–3 free quotes for this exact deck?

We'll send your plan to vetted local builders. Free, no obligation.

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).

Embed this calculator

One line. Any site. Free.

Drop the snippet into your contractor site, blog, or marketing page. Theme matches the parent site automatically.

<!-- Concrete Calculator — free embed by DeckMath -->
<a href="https://deckmath.com/calculators/concrete-calculator"
   data-deckmath-calc="concrete-calculator"
   data-theme="auto">Free Concrete Calculator by DeckMath</a>
<script src="https://embed.deckmath.com/v1.js" async></script>
One tool · free · no signup

Plan the whole project, not just one number

The Deck Project Planner turns your dimensions into a complete material list, cost, 3D preview, and a PDF you can take to the lumber yard — all in one place.

Open the plannerFind my material

Related

More calculators you'll need.

Concrete Bag Calculator

Bag-count optimizer for post holes, slabs, sonotubes, pier blocks. 15 SKUs across Quikrete + Sakrete + generic in 40-90 lb sizes. Pallet pricing tiers + mixer rental advisory + ready-mix breakpoint.

Footing Depth Calculator

Per-footing IRC R507.3 sizer: depth from frost + structural, diameter from soil bearing, rebar spec, concrete order. 5 soils × 4 footing types.

Frost Depth Calculator

IRC R403.1.4 footing-depth lookup. State + 80+ metro lookup, soil + elevation refinement, FPSF strategy. Free + free forever.

Deck Footing Calculator

Footing diameter, depth, concrete volume, and bag count — IRC R507.3 sized + frost depth lookup for all 50 states.