Concrete Bag Calculator

Under 1 cubic yard: bags are cheaper. Above 1 cubic yard (45 bags of 80 lb): ready-mix usually wins on total cost AND labor time. A 1 cuyd ready-mix delivery is $165-290 (region-dependent) plus $50-100 short-load fee. 45 bags at single-bag pricing is $335; at pallet-60 pricing (12% off) it's $295 — but you've also lost a Saturday to mixing. Above 2 cubic yards, ready-mix is the only sensible choice. The calculator shows a ready-mix advisory at the 1 yd³ breakpoint.

Both are essentially identical (Portland cement + sand + gravel premix). Quikrete is the dominant brand at Home Depot; Sakrete is the dominant brand at Lowe's. National-average pricing: Quikrete 80 lb ≈ $7.45, Sakrete 80 lb ≈ $7.25 (Sakrete typically 2-5% cheaper). Sakrete also sells Maximizer — an 80 lb bag with 25% higher yield (0.75 cf vs the standard 0.60 cf) at ~$9.95. If yield-per-bag matters more than per-bag price, Maximizer wins. Generic store-brand bags (Home Depot Build-It-Yourself, Lowe's UltraTech) save another 10-15% but have slightly lower compressive strength (3500 psi vs Quikrete/Sakrete 4000 psi).

Fast-set (Quikrete Fast-Setting, Sakrete Fast-Setting) is engineered for post-hole pours where you can't brace the post for 24 hours. Procedure: plumb the post in the hole, dump the dry bag in around it, then pour in water at the spec rate. Sets in 20-40 minutes; full strength at 28 days. NOT ideal for slabs — you can't trowel-finish a slab that's setting in 20 minutes. Bad choice for any pour bigger than ~4 cf at once. The calculator flags fast-set chosen for slab pours over 4 cf.

Quikrete 80 lb standard: ~0.60 gallons (~4.5 pints) per bag. 60 lb: ~0.45 gallons. 40 lb: ~0.30 gallons. Sakrete is virtually identical. Fast-set varies: ~0.40 gallons per 50 lb bag. Always start with about 80% of the spec water, mix to oatmeal consistency, then add the last 20% gradually. Too much water reduces compressive strength dramatically — a 1.5× water ratio can cut 28-day strength by 30%. The calculator reports total gallons needed across all bags.

IRC R507.3 requires 3000 psi minimum, so standard 4000 psi bags (Quikrete + Sakrete both rate at 4000 psi) easily exceed code. 5000 psi (Quikrete 5000, Sakrete Maximizer) is overkill for residential deck footings but recommended for: footings supporting hot-tub or pergola point loads, heavy stone-veneer column footings, or footings in cold-climate freeze-thaw zones (the higher psi resists freeze-thaw spalling). For a typical 36″ deep × 12″ Ø sonotube footing under a 12×12 PT deck, standard 4000 psi is fine.

Home Depot + Lowe's both publish pallet pricing — typically a 7% discount at 30+ bags and a 12% discount at 60+ bags. At the contractor desk, ask for 'pallet pricing on bagged concrete' — they'll quote the bulk rate, often with free truck loading. Below 30 bags you pay shelf price. The calculator auto-detects when your bag count crosses the threshold and shows the effective per-bag price + total discount. For deck projects averaging 25-50 bags, hitting the 30-bag tier is usually worth bumping the waste factor or adding 5 extra bags for a free 7% off.

Waste factor. Concrete pours always lose some material — spillage during mixing, form leakage, irregular hole walls, finishing scrap. Default 10% waste covers normal install. Bump to 15% for first-timers, irregular pours, or hot weather (set time pressure forces faster pours = more spillage). Drop to 5% only for clean, repeating pours by experienced installers (e.g. 20 identical sonotube footings). The bag count rounds UP from the wasted volume divided by per-bag yield.

Under 10 bags: hand mix in a wheelbarrow with a hoe. 10-25 bags: doable by hand but exhausting (each 80 lb bag = ~10 min of mixing). 25+ bags: rent a tool-mixer ($65/day at Home Depot Tool Rental). A 6 cuft tow-behind mixer fills 4 bags per batch, ~2 min per batch — 25 bags is ~12 minutes of mixing vs ~4 hours by hand. The calculator advises mixer rental at 25 bags and excludes fast-set bags (which don't need mixing — dry-pour method).

Light load (you can step on it, place forms above): standard mix 24 hours; fast-set 4 hours. Full design strength (28-day cure): 28 days for all mixes. For deck footings: you can frame on top of footings at 24 hours but don't fully load the deck (decking + railing) until 7-day strength (~70% of design strength). Cold weather (<50°F) extends all cure times significantly — 1.5-2× longer at 40°F. The calculator reports both light-load and full-strength cure hours per chosen mix.