Concrete
Concrete Slab Thickness: A Practical Guide
How thick should a concrete slab be? Practical thickness ranges for patios, walkways, shed bases, driveways and garage floors, plus how thickness affects cost.
3 min read
- Dual US / Metric
- +5% Waste Allowance
- Free · Runs in Your Browser
Concrete Cost Calculator
This calculator turns slab dimensions into a concrete order and a budget. Enter your local ready-mix price, and optionally delivery fees, reinforcement and labour, to see the total cost, the cost per square foot (or square metre) and how bagged concrete compares.
Enter your measurements
Enter your measurements and press Calculate to see quantities, a material breakdown and an optional cost estimate.
How the calculation works
- Volume = Length × Width × Thickness × (1 + Waste %)
- Concrete cost = Volume × Price per yd³ (or m³)
- Total = Concrete cost + Delivery + (Area × Rebar price) + (Area × Labour price)
- Cost per ft² = Total ÷ Area
Ready-mix is priced by volume, while reinforcement and labour are usually quoted per square foot or square metre, so the calculator applies each price to the right quantity.
No price is pre-filled. Concrete prices vary a lot between regions and suppliers, so use a quote from your area.
Assumptions used
- Prices you enter are applied as given. Tax, pumping, forms, base gravel and finishing extras are excluded unless included in your prices.
- Bag yields are typical label values; check the yield printed on the product you buy.
Example calculation
A 20 × 12 ft patio, 4 in thick, with 5% waste, ready-mix at $150 per yd³ and a $100 short-load fee.
- 1Volume: 20 × 12 × (4 ÷ 12) = 80 ft³ = 2.96 yd³
- 2With 5% waste: 3.11 yd³
- 3Concrete: 3.11 × $150 = $466.67
- 4Total with delivery: $566.67
- 5Per square foot: $566.67 ÷ 240 ft² = $2.36
Result: About $567 for materials and delivery, or $2.36 per ft².
How to measure your project
- Measure the length and width of the formed area, not the excavation.
- Check slab thickness at several points. A slab that is ½ in thicker than planned needs about 12% more concrete at 4 in.
- For L-shaped or irregular slabs, split the area into rectangles and run the calculator for each.
Frequently asked questions
How much does a yard of concrete cost?
It depends on your region, mix strength, order size and delivery distance, so ask two or three local ready-mix suppliers for a quote. Small orders often carry a short-load fee, which can noticeably raise the cost per yard.
Is it cheaper to use bags or ready-mix?
For small jobs, often under about 1 yd³ (0.75 m³), bags can be cheaper because there is no delivery or short-load fee. For larger pours, ready-mix is usually cheaper and far less work. Enter a bag price to compare both for your project.
Does the estimate include labour?
Only if you enter a labour price. Leave it blank for a DIY materials budget, or add a contractor's price per square foot or square metre for an installed estimate.
Why add a waste allowance to the cost?
Uneven ground, form bulges and spillage use extra concrete. Ordering 5–10% extra costs less than a second delivery or a cold joint from running short mid-pour.
Related guides
ConcreteHow Much Concrete Do I Need for a Concrete Slab?
Learn how to calculate concrete for a slab step by step, convert to cubic yards or cubic metres, add the right waste allowance and decide between bags and ready-mix.
3 min read
Results are estimates based on the measurements and assumptions you enter. Always confirm product specifications, local building codes and final quantities with your supplier or a qualified professional. See our disclaimer.