Concrete Slab Wizard

Draw your slab, answer a few questions, and get a complete materials list, tool list, cost estimate, and step-by-step plan.

1. Draw your slab
Drag on the grid to draw. Snap shapes together, weld them into one slab, and hover a shape to add a connected piece with the +.

Add shape

Layers

0'5'10'15'20'25'0'5'10'15'12' × 12'
2 ft
grid = 1'· two fingers to pan & zoom control joints

Selected shape

Select a shape to edit its size, snap it to others, or weld it into one slab.

Arrows nudge · ⌫ delete · ⌘C / ⌘V copy & paste

2. Answer a few questions
Tell us what the slab is for and we'll suggest a thickness, base, strength, and reinforcement — override anything.

Furniture and foot traffic. Wire mesh keeps it flat.

Suggested 4"
Sold by the cubic yard; short-load fees apply under ~5 yd.

Vapor barrier

6-mil poly under interior / enclosed slabs

Include tool rental in total

Add advisory rental/buy estimates to the grand total

Extra concrete for spillage and uneven subgrade. 10% is typical.

3. Your plan
Materials, tools, cost, and a step-by-step build plan. Every unit price is editable.

Concrete

1.96 yd³

Footprint

144 ft²

Perimeter

48 ft

Concrete$330

Ready-mix concrete (3000 psi)

2 cu yd · Ordered by the cubic yard, delivered. Short-load fees apply under ~5 yd.

Alt: Bagged: 88 x 80 lb bags

$330

Base & membrane$88

Compactable gravel base (4")

2.5 tons · 1.78 cu yd of crushed stone / road base, compacted in lifts.

Alt: Recycled concrete aggregate (often cheaper by the ton)

$88

Reinforcement$67

Welded wire mesh (6x6 W1.4)

7 sheets · Flat sheets lay flatter than rolled mesh. Overlap one square.

Alt: Rebar #3 grid (see rebar option)

$63

Mesh chairs / raisers

12 each · Keep mesh off the subgrade, in the slab's middle.

$4

Forms$100

Form boards (2x4)

7 8 ft boards · ~48 linear ft of edge form around the slab.

Alt: Reusable metal forms (rent) for large/curved pours

$42

Form stakes

28 each · One every ~2 ft plus corners. Wood or steel.

$49

Form screws

1 box · Screws (not nails) make stripping forms painless.

$9

Finishing$10

Expansion / isolation strip

2 8 ft strips · Where the slab meets a house, footing, or existing slab.

$10

Materials$595
Tool rentalnot in total$185
Estimated total$595

From US average prices — click any price to match a local quote. Excludes delivery, permits, and labor.

Tools you'll need

  • WheelbarrowMove and place the concrete.
  • Screed board (straight 2x4)Longer than the form is wide.
  • Plate compactorrent ~$70/dayCompact the gravel base in 2" lifts.
  • Bull floatrent ~$55/dayFlatten and close the surface after screeding.
  • Magnesium hand floatDetail work and edges.
  • EdgerRounds and strengthens the slab perimeter.
  • GrooverTools control joints into the wet slab.
  • Shovel, steel rake & margin trowelSpread, pull, and detail the pour.
  • Gloves, eye protection & rubber bootsWet concrete is caustic — cover up.
  • Concrete saw + diamond bladerent ~$60/dayOnly if you cut control joints the next day instead of tooling them wet.

Rental prices show only for specialty gear — skip them if you already own it.

Step-by-step plan

Your build, tracked

Save this plan to Blueprint

Turn your slab into a project with the full step-by-step plan, tool list, and shopping list you can check off as you build — about $595 in materials.

About the concrete slab calculator

Overview

Most slab calculators ask for one length and one width. Real slabs are rarely a plain rectangle: patios wrap around corners, garage pads have notches, and driveways flare at the apron. This tool lets you draw the actual footprint — rectangles, L-shapes, curves, and cutouts — then computes the exact concrete volume, gravel base, reinforcement, form lumber, tools, and a step-by-step pour plan.

Pick what the slab is for and it suggests a code-typical thickness, base depth, strength, and rebar grid, all of which you can override. Every material quantity is deterministic (no guessing), and every unit price is editable so the cost estimate matches your local supplier. When you like the plan, save it to a Blueprint project to track the build.

How to use this tool
  1. Drag on the grid to draw your slab, or add rectangle, semicircle, quarter-round, and triangle shapes and butt them together for L, T, or U shapes.
  2. Click any shape to set its exact width, length, and position, or to rotate curved shapes.
  3. Choose the slab's purpose — it sets a suggested thickness, gravel base, strength, and rebar grid you can override.
  4. Add optional structural elements (stairs, columns, footings) if your pour includes them.
  5. Review the materials, tools, and cost, adjusting any unit price to a local quote, then follow the step-by-step plan or save it to Blueprint.
Frequently asked questions

How much concrete do I need for a slab?

Multiply the footprint area by the thickness, then convert to cubic yards (divide cubic feet by 27) and add ~10% for waste. A 12x12 ft slab at 4 inches is about 1.8 cubic yards including waste. This tool does it automatically for any shape and shows both ready-mix cubic yards and equivalent bag counts.

How thick should a concrete slab be?

4 inches for walkways, patios, and shed floors; 5 inches for garage floors; 4-6 inches for driveways depending on vehicle weight; 6 inches or more for RV parking and heavy loads. Footings are typically 8 inches or thicker. The tool suggests a thickness from the slab's purpose and lets you override it.

Do I need rebar or wire mesh in a slab?

Driveways, garage floors, and structural slabs should have a rebar grid (commonly #4 at 18 inches on center). Patios and walkways on stable, well-compacted ground can use welded wire mesh or fiber added to the mix. The tool estimates rebar sticks, chairs, and tie wire, or mesh sheets, based on your choice.

How much gravel base goes under a slab?

A 4-inch compacted crushed-stone base is standard for slabs on grade, 6 inches for driveways or poor soils. Compact it in 2-inch lifts. The tool converts your base depth and footprint into tons of gravel.

Is the cost estimate accurate?

It starts from US average unit prices and is fully deterministic, but concrete pricing is regional and delivery/short-load fees vary. Every unit price in the results is editable, so drop in quotes from your local ready-mix plant and building-supply store for a precise number.

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