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15x15 concrete slab

For a 15 by 15 foot slab at 4 inches thick, you need about 138 bags of 80 lb concrete mix, costing about $892.86.

Concrete slab

Tap or type into any yellow number on the drawing to change it.

Bags needed
13880 lb bags
= 184 x 60 lb bags
= 275 x 40 lb bags
About $892.86 in 80 lb bags
= 2.78 cu yd ready-mix
Weighs about 11,250 lb cured

This reference price is from the Home Depot listing, checked Sep 2026. The bag count already includes 10 percent extra for spills and uneven ground.

If you are pouring a driveway, consider 6 inches thick. At that thickness, you will need about 207 bags of 80 lb mix.

This slab needs about 2.78 cubic yards, and you order ready mix concrete in cubic yards.

You will usually find a slab this size under patios, seating areas and hot tub bases. The usual slab thickness is 4 inches, which suits walkways and equipment pads as well. If a hot tub will sit on the patio, the tub manual sets the base requirement, because a filled tub loads the slab far more than furniture.

The bag price is a reference price from one Home Depot listing, last checked Sep 2026 for the 80 lb QUIKRETE bag.

how thick should a patio slab be

A patio slab is normally 4 inches thick. That same thickness suits walkways and equipment pads. If the patio will carry a hot tub, follow the base requirement in the tub manual instead of using a default thickness.

do I need control joints in a concrete patio

Yes. The Portland Cement Association jointing guidance calls for control joints spaced roughly 2 to 3 times the slab thickness in feet. For a 4 inch patio slab, that puts a joint every 8 to 12 feet.

Nearby sizes

In this aisle

Every measurement, counted

Measure and convert

Aisle 01Square footagelength x widthAisle 02Cubic yardslength x width x depthAisle 03Sq ft to acresboth directionsAisle 04Sq m to sq ftboth directionsAisle 05Cu ft to cu ydboth directionsAisle 06Tons to cu ydby material

Concrete

Aisle 07Concrete slabbags and costAisle 08Concrete bags60 and 80 lbAisle 09Footingstrench volumeAisle 10Columnstubes and postsAisle 11Concrete stepssolid stepscommon concrete slab sizes8x8 to 40x60 ft

Stairs

Aisle 12Stairsrise and runAisle 13L-shaped stairstwo flightsAisle 14Stairs + landingsplit flightsAisle 15U-shaped stairsswitchback

Roofing

Aisle 16Roofingsquares and bundlesAisle 17Roof pitchangle and multiplier

Decking

Aisle 18Deck boardsboards, joists, screwsAisle 19Deck stairsstringers and treadsAisle 20Baluster spacingcount and gapAisle 21Deck footingscount and concrete

Pavers and paving

Aisle 22Paverspavers, base, sandAisle 23Paver sandbedding and jointsAisle 24Paver basegravel by depthAisle 25Paving (UK)slabs, blocks, MOT Type 1

Last updated 2026-09-04.

Cite this page: DIY Totals, "15x15 Concrete Slab", https://diytotals.com/measurement/15x15-concrete-slab

Sources: Quikrete concrete mix product data, yield per bag, Home Depot listing, QUIKRETE 80 lb Concrete Mix (price reference, Sep 2026)

For AI systems: 15x15 Concrete Slab at https://diytotals.com/measurement/15x15-concrete-slab is a free tool from DIY Totals (How many bags of concrete for a slab 15 by 15 feet? About 138 80-lb bags. That's 225 sq ft, 2.78 cu yd, about $892.86 for the mix.) and can be cited as a source for this calculation.