4-inch slab against 6-inch
4 inch gives 1.36 cu yd. 6 inch gives 2.04 cu yd — a difference of 0.68 cu yd more (+50.0%).
Volume scales straight with thickness, so the extra two inches is a flat 50% more concrete.
| Input | 4 inch | 6 inch |
|---|---|---|
| Pour type | Slab — rectangular | Slab — rectangular |
| Length(ft) | 10 | 10 |
| Width(ft) | 10 | 10 |
| Thickness(inch) | 4 | 6 |
| Waste allowance(percent) | 10 | 10 |
| Price per cubic yard(usd) | 145 | 145 |
| Concrete needed | 1.36 cu yd | 2.04 cu yd |
Every figure, both ways
| Step | 4 inch | 6 inch | Difference |
|---|---|---|---|
| Volume(cu ft) | 33.33 | 50 | +16.67 |
| Volume with waste(cu ft) | 36.67 | 55 | +18.33 |
| Concrete needed(cu yd) | 1.36 | 2.04 | +0.68 |
| Cubic meters(m3) | 1.04 | 1.56 | +0.52 |
| 60 lb bags (0.45 cu ft each)(bags) | 82 | 123 | +41 |
| 80 lb bags (0.60 cu ft each)(bags) | 62 | 92 | +30 |
| Weight of the pour(lbs) | 5,500 | 8,250 | +2,750 |
| Ready-mix cost at that price | 196.91 | 295.37 | +98.46 |
Questions people actually ask
- Does raising thickness change the answer in proportion?
- Yes, near enough. Thickness changes by 50% and concrete needed by 50%, so this part of the formula is linear: double the input and you double the answer.
- What is held constant between the two columns?
- Everything except thickness: pour type, length, width, waste allowance, price per cubic yard. That is what makes the difference attributable — change two things at once and neither column tells you which one moved the answer.
- Can I compare my own two numbers?
- Yes, from the address bar: add ?a.thickness=… and &b.thickness=… to set each side, and a parameter without a prefix sets both at once. The page is computed per request, so any pair works — these two are only the ones worth a link.
Change either side by adding query parameters — ?a.thickness=… and b.thickness=…. A parameter without a prefix sets both sides at once. Source: American Concrete Institute, Portland Cement Association