Concrete Bag Calculator
Bag-count optimizer for small-to-medium concrete pours. Pick your pour type (post holes, pier blocks, slab, sonotube, custom volume), dimension it, pick brand + bag size + mix grade — calculator returns bag count with waste, pallet pricing tier (single / pallet-30 7% off / pallet-60 12% off), water gallons, cure time, mixer-rental advisory at 25+ bags, and a ready-mix breakpoint alert at 1 cubic yard.
Inputs
Hole dimensions
Cylindrical hole around post
Bag selection
15 SKUs · Quikrete / Sakrete / generic
Pricing + mix check
Bag selection + volume look good
Bag count + mix grade check24 bags of 80lb Quikrete (4000 psi, 0.6 cf/bag yield). 12.6 cf total · 0.47 yd³.
Quikrete Concrete Mix 80lb — most popular
Bill of materials
Pouring more than 1 yd³?
The Concrete Calculator handles ready-mix delivery vs bag math for full footing + slab projects. Above 1 yd³ delivered concrete is usually cheaper AND faster than bags.
Bag yields per Quikrete + Sakrete published spec sheets (2026-Q1). Pricing reflects national-average retail at single-bag pricing; pallet tiers track Home Depot + Lowe's published bulk discounts. DeckMath is not a substitute for a licensed structural engineer.
How to use
Three steps. Permit-ready output.
- 01
Pick your pour type
Post holes (cylindrical, with optional 4×4 / 6×6 post displacement deducted), pier-block / footing pads (typical 12×12×8″ small footings), slab pours (L × W × thickness), sonotubes (cylindrical deck footings — no post displacement), or custom volume (enter cubic feet directly).
- 02
Dimension the pour
Post hole + sonotube: diameter + depth + count. Slab: length × width × thickness. Pier block: number of blocks. Custom: just enter total cubic feet.
- 03
Pick brand + bag size
Quikrete, Sakrete, or generic. Bag sizes 40 lb (0.30 cf yield) through 90 lb (0.675 cf yield). Sakrete Maximizer 80 lb has 25% higher yield (0.75 cf per bag) — counts as high-strength grade.
- 04
Pick mix grade
Standard (3000-4000 psi general purpose), high-strength (5000 psi for structural footings + slabs), fast-set (post holes — sets in 20-40 min, no propping needed), crack-resistant (fiber-reinforced for thin slabs).
- 05
Adjust waste factor
Default 10% covers normal spillage + dimensional rounding. Bump to 15% for irregular pours or DIY first-timers. Drop to 5% for clean, well-formed pours by experienced installers.
- 06
Read your BoM
Bag count + pallet-pricing tier + water gallons + cure time. Look for the mixer-rental advisory (kicks in at 25+ bags) and the ready-mix breakpoint alert (above 1 cubic yard bag-buying is usually more expensive than calling for delivery).
How we calculate
The math, fully transparent.
The Concrete Bag Calculator is a bag-count optimizer for small-to-medium concrete pours where you're buying bags off the pallet — fence post holes, deck pier-block sets, walkway slabs, sonotube footings, repair pours. Pick your pour type, dimension it, pick a bag SKU (Quikrete, Sakrete, or generic across 40-90 lb sizes and Standard / 5000 psi / Fast-Set / Crack-Resistant grades), and the calculator returns bag count with waste, pallet-pricing tier (single / pallet-30 / pallet-60), water required, cure time, mixer-rental advisory, and a ready-mix breakpoint alert when bag-buying stops making economic sense.
IRC references
- IRC R507.3 — Deck footings: 3000 psi minimum compressive strength concrete
- IRC R403.1.4.1 — Frost depth: post holes for deck footings must extend below local frost line
- ACI 332 — Residential code requirements for structural concrete
- Manufacturer published yield + water-content specs (Quikrete + Sakrete spec sheets, 2026-Q1)
Bag yields from Quikrete + Sakrete published spec sheets. Pallet pricing tiers track Home Depot + Lowe's published bulk discounts (7% at 30+ bags, 12% at 60+). Mixer rental cost from Home Depot Tool Rental national average. Ready-mix breakpoint per industry-standard $/yd³ comparison.
12″ diameter × 36″ deep = π × 0.5² × 3 = 2.36 cf gross. 4×4 post (3.5″×3.5″ = 0.0851 sqft) embedded 36″ displaces 0.26 cf — so net concrete needed is 2.10 cf per hole. 6×6 post displaces 0.63 cf for the same depth.
8 ft × 4 ft × 4″ slab = 32 × 0.333 = 10.67 cf. At 0.60 cf yield per Quikrete 80 lb bag + 10% waste, that's ceil(10.67 × 1.10 / 0.60) = 20 bags.
Yield is the cured-concrete cubic-foot output per bag — published on every Quikrete / Sakrete spec sheet. 80 lb bag = 0.60 cf, 60 lb = 0.45 cf, Sakrete Maximizer = 0.75 cf per 80 lb bag. Waste covers spillage + form irregularity.
Home Depot + Lowe's both publish pallet-quantity discounts. 30-bag tier saves ~7% (typical $0.50 / bag), 60-bag tier saves ~12% (typical $0.85 / bag). Below 30 bags = pay sticker. The calculator auto-applies the right tier.
Hand-mixing 25+ bags is ~6 hours of grueling labor. A $65/day rental tool-mixer cuts that to ~1.5 hours and gives a more consistent mix. Fast-set bags skip mixing (pour dry into hole, add water — that's the entire point of fast-set) so this advisory excludes that grade.
1 cubic yard ≈ 45 bags of 80 lb concrete = $335 in bags ($300+ if pallet-discounted) + your weekend. Ready-mix delivery is $165-290 / yd³ in 2026 (region-dependent) plus a $50-100 short-load fee under 3 yd³. Once you cross 1 yd³, delivered concrete is usually faster AND cheaper. Use the Concrete Calculator (yardage focus) for the comparison.
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Frequently asked
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