10x12 Concrete Slab Calculator: 1.63 yd3, 74 Bags, Cost

A 10 ft x 12 ft concrete slab at 4 inches thick needs about 1.63 yd3 of concrete with 10% waste, or roughly 74 common 80-lb bags. At a hypothetical USD 165 per yd3 plus USD 125 delivery, the concrete and delivery example is $393.89. This is not an installed price or a local quote: the 120 sq ft slab still needs a written scope for preparation, reinforcement, placement, finishing, cleanup, taxes, and any supplier minimums.

Use the Concrete Slab Calculator for exact dimensions, the Concrete Cost Calculator for local material assumptions, and the Concrete Quote Reviewer when a contractor bid says "10x12 slab" but does not spell out the base, thickness, reinforcement, finish, and delivery scope. If you only need the bag-count answer, use How Many Bags of Concrete for a 10x12 Slab?.

10x12 slab answer in one screen

Use the quantity as a starting point, then compare the actual buying and installation scope. Displayed yards are rounded; bag counts and example costs use the unrounded volume.

The useful decision is not only the yardage. A 10x12 slab is small enough that ready-mix may trigger a short-load or minimum-order fee, but large enough that 74 heavy bags can create mixer fatigue, cold joints, and pickup payload issues.

Thickness, bags, and cost table

These planning numbers use one 10% allowance, assumed yields of 0.60 ft3 per 80-lb bag and 0.45 ft3 per 60-lb bag, and hypothetical USD 165 per yd3 plus USD 125 delivery. The delivery charge is already included in each dollar total; no supplier minimum, order increment, tax or additional fee is assumed.

These are arithmetic examples, not current supplier prices. A shed pad, patio base, hot-tub pad, or small shop slab can have different requirements for excavation, gravel, reinforcement, drainage, access, and finish.

Formula for a 10x12 concrete slab

area = length ft x width ft
depth ft = thickness in / 12
volume ft3 = area x depth ft
allowance ft3 = volume ft3 x 1.10
order yd3 = allowance ft3 / 27

At 4 inches:

10 x 12 x (4 / 12) = 40 ft3
40 x 1.10 = 44 ft3
44 / 27 = 1.629629... yd3

The display rounds this to 1.63 yd3. To calculate bags, divide the unrounded 44 ft3 by the yield printed on the product, then round up once to whole bags:

44 / 0.60 = 73.333... bags
round up = 74 bags
cost = (44 / 27) x 165 + 125
cost rounded to cents = $393.89

Do not multiply the displayed 1.63 yd3 by the unit price or add a second 10% allowance. At 5 and 6 inches, the volumes with allowance are 55 and 66 ft3; those unrounded quantities produce the table's prices. In a real order, use the supplier's agreed quantity increment and minimum billable quantity. A larger billed quantity does not automatically mean that much is delivered.

For a shed-specific version of this decision, see the Concrete Shed Base Calculator and the Shed Base Concrete Mix Calculator Guide.

Bags vs ready-mix for a 10x12 slab

A 10x12 slab needs a crew and access plan as well as a material price. There is no universal area or bag-count threshold at which one supply method wins.

If the slab is behind a house, check the Concrete Wheelbarrow Distance Calculator before assuming the truck can reach the forms. If the quote lists ready-mix separately, normalize the delivered total with the Concrete Ready-Mix Near Me Quote Script.

Quote scope for a 10x12 slab

Two bids can both say "10x12 concrete slab" and still include different work. Ask for the scope in writing before comparing totals.

For example, a hypothetical all-in USD 1,800 bid divided by 120 sq ft is USD 15 per sq ft. That division normalizes a quote; it does not establish a market rate or say what is included. Compare only bids with the same scope, and do not add material or delivery again if it is already in the bid.

Use the Concrete Scope of Work Checklist to compare bids line by line. If the slab will carry a vehicle, hot tub, shed, or shop equipment, also check thickness, base, and reinforcement with a qualified local professional before ordering.

Ask whether a ready-mix quote uses ordered yards, minimum billable yards, a minimum invoice total, or a fixed delivered price. Add only charges that apply and are not already included. Confirm delivery, short-load, waiting time, tax and access charges separately; do not assume all suppliers stack them.

Sources and checks

This page uses geometric quantities and explicitly hypothetical prices. Product yield, local ready-mix pricing, site access, and installed labor must be confirmed before buying concrete. Source context was reviewed September 10, 2026; none of these links establishes a current local bid for this slab.

FAQ

How much concrete do I need for a 10x12 slab?

At 4 inches thick, plan about 1.48 yd3 before waste or 1.63 yd3 with 10% waste. At 5 inches, plan about 2.04 yd3 with waste. At 6 inches, plan about 2.44 yd3 with waste.

How many 80-lb bags for a 10x12 slab?

At 4 inches thick with 10% waste, buy about 74 common 80-lb bags. At 5 inches, buy about 92 bags. At 6 inches, buy about 110 bags.

How much does a 10x12 concrete slab cost?

At 4 inches, the hypothetical concrete-and-delivery example is $393.89: 44 ft3 divided by 27, multiplied by USD 165 per yd3, plus USD 125 delivery. It excludes supplier minimums, tax and installation. An installed price requires a local bid covering preparation, reinforcement, placement, finish and the other agreed work; a generic square-foot rate cannot determine it.

Is a 10x12 slab too big for bags?

It can be poured with bags, but 74 80-lb bags is heavy work. Compare store delivery, mixer rental, labor, finish timing, and ready-mix minimums before checkout.

Should a 10x12 slab be 4 inches or 6 inches thick?

Four inches is a common planning starting point for light slabs. Vehicle loads, hot tubs, shed weight, shop equipment, soil, frost, base prep, and local rules can require a thicker or engineered slab.

Next step

Run the exact dimensions in the Concrete Slab Calculator, compare bagged and ready-mix totals in the Ready-Mix vs Bags Calculator, then review the written bid in the Concrete Quote Reviewer.