Cost to Pour a 100 Sq Ft Concrete Slab: $400 to $800

The Contractor Minimum Dominates at This Size

The national average installed cost for a 4-inch wire-mesh concrete slab is $6.50 per square foot. Multiplied across 100 sq ft, that suggests $650 for the pour. In practice, real quotes for a 100 sq ft pad cluster between $400 and $800, with a notable jump compared to the same per-sq-ft math applied to a 1,000 sq ft pour. The reason is the contractor's minimum mobilisation fee, which covers the fixed cost of getting a crew, a ready-mix truck, and forming materials to your site regardless of how small the actual pour is.

Industry-wide, the residential mobilisation minimum runs $400 to $800, with most contractors landing at $500 to $600. The fee is rarely shown as a separate line on the quote; it is baked into the per-sq-ft headline number, which is why a 100 sq ft pour quotes around $8 per sq ft (apparent) when a 1,000 sq ft pour from the same contractor quotes around $5.50 per sq ft. The crew is the same, the concrete is the same per cubic yard, but the fixed overhead is amortised across a tenth as many square feet.

This is why bundling small pours into larger jobs is the single biggest cost-saver. If you have a 100 sq ft AC pad to install and a driveway extension or patio project planned within the next year, pour the AC pad as part of the larger job. The marginal cost of the 100 sq ft drops from $400 to $800 to around $150 to $300 because the mobilisation fee is already spent. The same logic applies to combining a hot tub pad with a patio expansion, or a shed pad with a walkway repour.

10x10, 8x12, or 5x20: Which Shape for the Use Case

One hundred square feet can be poured as a square (10x10), a moderately-rectangular shape (8x12 at 96 sq ft, or 8x13 at 104 sq ft), or a long strip (5x20). Each shape suits a different application. The square works best for a hot tub base, AC condenser pad, generator pad, or small storage shed because the proportions match the equipment footprint. The moderate rectangle works for a small workshop entry or garden-shed pad with a forward-bias door swing. The strip works for a walkway extension, RV step-out pad, or boundary path between gate and door.

From a cost perspective, the differences are real but small at this scale. A 10x10 has a perimeter of 40 ft, requiring 40 ft of 2x4 or 2x6 forming lumber, 8 stakes (at corners and midpoints), and roughly 30 minutes of forming labour. An 8x12 has a perimeter of 40 ft (same). A 5x20 has a perimeter of 50 ft, requiring 25 percent more forming lumber and 10 stakes, with roughly 40 minutes of forming labour. The cost difference is $10 to $20 in materials and $20 to $40 in labour, modest in the context of the total project budget.

The bigger consideration is concrete pour logistics. A long 5x20 strip is harder to screed and finish in one go because the screed board has to travel 5 ft of width across 20 ft of length, requiring more passes and more attention to the leading edge. A 10x10 square can be screeded in a single pass with a 12-ft screed board, making it the easier DIY shape. If you're hiring a contractor, the shape difference doesn't affect their pricing materially. If you're pouring it yourself, default to the 10x10 unless the use case demands the rectangle or the strip.

Pouring a 100 Sq Ft Pad Yourself: What to Buy

The DIY path for a 100 sq ft slab needs three categories of supply: concrete material, sub-base material, and forming material. For concrete, 100 sq ft at 4 inches thick is 1.23 cubic yards or 33.3 cubic feet. Bagged concrete at 80 lb per bag yields 0.6 cubic feet per bag, so you need 56 bags of 80 lb concrete mix. At Home Depot in 2026, an 80 lb bag of Quikrete or Sakrete runs $5.50 to $6.50, so the concrete bill is $310 to $365. Add 4 bags as a 10 percent buffer for spillage and consolidation, bringing the total to 60 bags or roughly $340 to $390.

For sub-base, you need approximately 1 cubic yard of crushed-stone gravel (3/4-inch aggregate, sometimes labeled "Class 5" or "ABC stone") for a 4-inch base. Bulk delivery from a local quarry runs $35 to $60 per cubic yard delivered. Bagged 50 lb gravel bags run $4 to $6 each and you would need roughly 40 bags, totaling $160 to $240, which is more expensive than bulk. For a 100 sq ft pour, bulk gravel is the better economics if your driveway can accept a small dump-truck delivery.

For forming, you need four 8-ft 2x4 or 2x6 lumber pieces ($25 to $40 total), eight 12-inch wooden stakes or rebar stakes ($10 to $20), a 50 ft roll of mason's line ($5), and some duplex nails or screws ($5). If you're adding wire mesh reinforcement (recommended for any slab that will see foot traffic or modest equipment loads), one 5x10 ft sheet of 6x6 #10 welded wire mesh runs $25 to $40, and you need two sheets to cover 100 sq ft with overlap. Total forming and reinforcement budget is $80 to $130.

Tool rental for the day adds $150 to $250: a plate compactor at $75 per day, a magnesium float at $15 per day, a steel bull float at $25 per day, a screed board at $15 per day (or you can use a straight 2x4), and a concrete edging tool at $15 per day. Total DIY cost: $570 to $760 in materials and rentals, plus 6 to 8 hours of labour for two people. Versus $400 to $800 for a contractor pour, the savings are modest, but the project is straightforward for a confident DIY-er. See the dedicated DIY tool rental cost breakdown for line-item rates.

Bagged vs Ready-Mix Truck Delivery at 100 Sq Ft

At 1.23 cubic yards, a 100 sq ft 4-inch pour sits right at the boundary where bagged concrete and short-load ready-mix delivery become roughly cost-competitive. Bagged at 60 bags of 80 lb costs $330 to $390. Short-load ready-mix delivery is typically priced at $130 to $200 per cubic yard for the concrete plus a $50 to $150 short-load fee (applied to orders under 5 cubic yards) and a $50 to $150 delivery fee. For 1.5 cubic yards (rounded up for the truck to deliver), that totals $295 to $450.

The ready-mix path wins on labour. Bagged concrete requires mixing 60 separate batches over 3 to 4 hours of continuous work (assuming one rented gas-powered mixer), whereas ready-mix is poured straight from the truck chute in 5 to 10 minutes. The mental and physical fatigue of bagged-mixing 60 bags is real and often underestimated by DIY-ers.

The ready-mix path loses on logistics. The truck cannot reach every site (steep driveways, narrow side gates, soft lawns are blockers). The truck arrives on a window, not a precise time, so you must be set up and ready when it arrives, with no flexibility. Bagged concrete gives you total control over timing and works in any site condition. For a 100 sq ft pad in an accessible driveway location, ready-mix is the better choice. For a 100 sq ft pad in a back garden behind a 36-inch gate, bagged is the only option.

The DIY Cutoff: When 100 Sq Ft Is Too Much to Pour Yourself

Most homeowners can pour a 100 sq ft pad with a helper over a Saturday. Some cannot, and the cutoff factors are predictable. The first cutoff is physical capacity: 56 bags of 80 lb concrete is 4,480 lb of material to move from delivery point to mixing point to the form. If you cannot move 4,480 lb of bagged material in stages over a few hours, hire the contractor. The second cutoff is timing pressure: once the first bag is mixed, you have roughly 90 minutes before that concrete starts to stiffen, and the entire pour must complete within that window. If you have not poured concrete before and the layout is irregular, the timing pressure can produce poor finishes.

The third cutoff is the use case. A hot tub pad must be perfectly level and structurally rated for 5,000 lb of filled weight; mistakes are expensive to fix and can compromise the hot tub. A generator pad must be perfectly level for the generator's resonance control. Equipment pads that bear significant loads or that must remain perfectly flat for years should be poured by a contractor or by an experienced DIY-er with at least two prior concrete projects. A shed pad or an AC condenser pad has more tolerance for minor imperfections and is a better first DIY project.

If you do hire a contractor for a 100 sq ft pad, expect the quote at the high end of the per-sq-ft range and recognise it reflects mobilisation cost rather than the contractor padding the bid. Get three quotes anyway: the lowest will often be from a contractor whose minimum is structured around small jobs, and the highest will often be from a contractor whose business is patios and driveways. The DIY feasibility page has a more detailed go-no-go checklist.

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