Pour a concrete slab yourself, or hire a pro?

What the DIY column actually contains

That headline DIY figure is concrete plus a flat $100–$300 allowance for everything else. It is a reasonable rule of thumb on a small pad and it gets optimistic fast. Here is what “everything else” is, priced and counted per size:

Slab	Concrete delivered	Base gravel (4″)	Reinforcement	Forms
10×10 (100 sq ft)	≈ $298–$398	2 tons ≈ $100	3 mesh sheets or 9 × 20 ft bars	40 ft — 5 boards, 10 stakes
12×12 (144 sq ft)	≈ $380–$480	3 tons ≈ $150	4 mesh sheets or 12 × 20 ft bars	48 ft — 6 boards, 12 stakes
16×20 (320 sq ft)	≈ $743	6.5 tons ≈ $325	8 mesh sheets or 26 × 20 ft bars	72 ft — 9 boards, 18 stakes
20×20 (400 sq ft)	≈ $908	8 tons ≈ $400	10 mesh sheets or 32 × 20 ft bars	80 ft — 10 boards, 20 stakes
24×24 (576 sq ft)	≈ $1,320	11 tons ≈ $550	14 mesh sheets or 46 × 20 ft bars	96 ft — 12 boards, 24 stakes

The base is the line people leave out. Four inches of compacted crushed stone under a 24×24 slab is 11 tons, about $550 delivered — on its own, more than the whole extras allowance. Add the tool rental — $80/day for a plate compactor and $60/day for a concrete saw, $140 together — and gravel plus rental alone exceeds the $300 allowance from the 16×20 slab upward, before a single form board or sheet of mesh.

Two more line items that never appear in a materials estimate. Reinforcement support: mesh or rebar has to sit in the middle of the slab, so budget chairs or bar supports and roughly 361 tie-wire intersections on a 24×24 grid — mesh laid on the ground and walked on during the pour ends up at the bottom, carrying nothing. Disposal: digging out 8″ for slab and base on a 24×24 produces around 17.8 cubic yards of loose spoil — excavated soil bulks up by about a quarter and never fits back where it came from. That is a dumpster, several trailer loads, or somewhere on your property you are willing to lose.

The labour reality

Concrete does not wait. In warm weather it starts stiffening within about 30 to 60 minutes of leaving the drum, and anything you place after the previous batch has begun to set forms a cold joint — a visible line that is also a permanent weak line through the slab. So the question is not whether you can move the concrete, it is whether you can move it fast enough.

Slab	Weight on the ground	Wheelbarrow loads	Barrow time, one person	If you mix bags instead
10×10	≈ 4,667 lb	12	≈ 24–36 min	62 bags · 31 batches · ≈ 2.6 hr
12×12	≈ 6,720 lb	16	≈ 32–48 min	88 bags · 44 batches · ≈ 3.7 hr
16×20	≈ 14,933 lb	36	≈ 72–108 min	196 bags · 98 batches · ≈ 8.2 hr
20×20	≈ 18,667 lb	45	≈ 90–135 min	245 bags · 123 batches · ≈ 10.3 hr
24×24	≈ 26,880 lb	64	≈ 128–192 min	352 bags · 176 batches · ≈ 14.7 hr

A wheelbarrow of wet concrete is loaded to about 3 cubic feet — roughly 420 lb — because it is weight-limited, not volume-limited, and a full round trip is realistically two to three minutes over rough ground. From the 12×12 slab up, one person barrowing alone can use up the whole 45-minute working window just placing — before screeding, floating and edging, all of which have to happen while the concrete is still workable. This is why a truck pour is a crew job: someone placing, someone screeding, someone floating, all at once.

Mixing bags is worse, not better. The last column assumes a rented mixer at 2 bags a batch and about 5 minutes per batch to load, mix, dump and place. Past roughly 60 bags that stops being a realistic one-person plan — the first section is setting hard while you are still mixing the last, which is exactly how a slab ends up with cold joints running through it.

When DIY clearly wins

• Small, non-structural pads — shed bases, AC and generator pads, small walkways. Anything up to about 1.5 cubic yards is a single-session job you can place before it moves.
• You have 2–3 helpers. Concrete sets on its own schedule; even a 10×10 pour is a hard two- to three-person job from truck to finish.
• You've finished concrete before — screeding, floating, edging, and timing the trowel are learned skills, and a bad finish is permanent.
• Access is easy — the truck, or your wheelbarrow route, can get close to the forms without crossing a lawn or a gate.

When DIY clearly loses

• Anything structural or load-bearing — garage slabs, footings, driveways that carry vehicles. Thickness, base compaction, and reinforcement all have to be right, and they are checked by an inspector rather than by you.
• Big pours. Past roughly 2–3 yd³ the placing and finishing outrun a DIY crew before the concrete does — see the barrow times above.
• Sloped or poorly-draining sites — grading and drainage mistakes cost far more than the labour you saved.
• Permits and inspections apply. Pros know the local code for slab thickness, footing depth, and vapour barriers, and they know which of it gets inspected.

What a contractor's quote covers that a DIY estimate misses

The gap between the two columns at the top is not pure profit. Most of it is work that a materials estimate silently assumes is free:

• Excavation and haul-off — cutting to grade, and taking the spoil away. On a 24×24 that is roughly 17.8 yd³ of soil somebody has to move twice.
• Base placement and compaction in lifts — not just dumping gravel, but compacting it 2–3 inches at a time so it actually supports the slab.
• Thickened edges and footings. Anything with a wall on it needs a deepened perimeter. That concrete is over and above the flat-slab volume every calculator gives you, this one included, and it can add 15% or more.
• Finishing to a specification — screed, bull float, edge, joint, broom or power trowel, in the right order, in a window measured in tens of minutes.
• Curing and protection — plastic, blankets, or a curing compound, and coming back to check it.
• Insurance and a warranty. A contractor who gets the finish wrong fixes it. If you do, you own it — and removing a bad slab costs more than pouring the right one did.

How to check a quote

Concrete volume is one of the very few line items on a construction quote a homeowner can independently verify. Run your dimensions through the concrete calculator and compare. For a 24×24 at 4″ that is 8 cubic yards delivered, and a quote built on a wildly different figure deserves a question.

A quote above your number is not automatically padded. Thickened edges, footings, a deeper base, or a slab specified at 5–6″ instead of 4″ are all legitimate reasons for more concrete — and they are all things you want. What matters is whether the contractor can explain the gap in those terms. Someone who says “that's just what it takes” is guessing or hiding something; someone who says “you're at 8 yards flat, I've allowed for a 12-inch thickened edge under the wall line” is a contractor worth hiring. A quote well below your number is the more worrying direction — it usually means a thinner slab, a shallower base, or no reinforcement.

Questions to ask before you sign

Get every quote in writing, get at least three, and ask all of these. The answers differentiate bids far better than the price does:

• What thickness are you pouring, and what PSI mix? (4″ / 3,000–4,000 PSI is standard residential; anything carrying vehicles should be thicker.)
• How deep is the base, what material, and is it compacted in lifts?
• Is reinforcement included — mesh or rebar — and how is it held up off the subgrade?
• Are there thickened edges or footings, and are they in the quoted volume?
• Where will the control joints go, and are they saw-cut or tooled?
• What finish — broom, float, or trowel — and which way does the slab drain?
• Who removes the excavated soil, and is disposal in the price?
• What is the warranty, in writing, and what does it exclude? (Hairline shrinkage cracking is normally excluded everywhere.)

Comparing two or three local quotes is worth ten minutes either way: it prices your exact site, including the access and drainage problems no calculator can see, and if the quotes come back near your DIY cost, the decision makes itself.

Do the materials math first

Whichever way you lean, start with the exact quantity: the concrete calculator gives bags vs ready-mix and cost for your dimensions (or jump to a common size like a 10×10 or 20×20 slab), the how-much-concrete guide explains the math, concrete slab thickness covers the 4″ vs 6″ decision that drives most of the volume, and slab cost by size prices every footprint this site publishes. Knowing your materials number keeps any quote honest.