A 20 x 18 ft driveway. Five inches of concrete. The calculator says 6.11 cubic yards - that is 33 bags of Portland cement, 3.35 tons of sand and 5.92 tons of gravel sitting under a surface you park on every day. Total materials bill: $936. Labor adds another $397.
Most homeowners never see those numbers until the truck pulls up and the driver asks where to pour.
The roof above that driveway is worse. A standard gable - 18 ft of slope, 50 ft wide, two planes - covers 1,980 square feet. That translates to 60 bundles of asphalt shingles, 5 rolls of underlayment and a $14,652 installed price tag. And somewhere between the driveway and the roof, there are walls that need insulating - 303 square feet of fiberglass batts at R-13, five rolls, $514 all in.
Three jobs. Three calculators. One article.
4 inches vs 6 inches - the concrete thickness decision
Two inches should not matter much. They do.
A 4 inch slab is the residential minimum for foot traffic. Sidewalks, patios, garden paths - anything that carries people but not vehicles. A 6 inch slab is what driveways, garage aprons and any surface bearing vehicle weight actually needs.
Here is what that difference looks like for a 20 x 18 ft area:
| Parameter | 4 in (patio) | 5 in (garage) | 6 in (driveway) |
|---|---|---|---|
| Concrete volume | 4.89 cu yd | 6.11 cu yd | 7.33 cu yd |
| Cement bags (94 lb) | 27 | 33 | 40 |
| Sand | 2.68 tons | 3.35 tons | 4.01 tons |
| Gravel | 4.74 tons | 5.92 tons | 7.10 tons |
| Material cost | ~$749 | ~$936 | ~$1,123 |
| Best for | Patios, walkways | Garages, light vehicles | Driveways, trucks |
Going from 4 to 6 inches adds 50% more concrete. Not 50% more strength - actual compressive strength depends on the mix ratio - but 50% more material, cost and weight on the subgrade. A 5 inch slab splits the difference for garage floors where you park a sedan but never a dump truck.
The mix matters too. Standard (1:3:5) uses 250 kg of cement per cubic meter - fine for a patio. Medium (1:2.5:4) bumps that to 300 kg - the sweet spot for driveways. Strong (1:2:3) at 350 kg per cubic meter is structural territory: footings, columns, anything load-bearing. The calculator lets you switch between all three and watch the bag count change.
When do you need 8 or 12 inches?
Post footings for deck supports typically run 8 inches deep in a sonotube. Strip footings under load-bearing walls go to 10 or 12 inches, depending on soil bearing capacity and local code. At 12 inches, that same 20 x 18 ft footprint would swallow almost 15 cubic yards - a full truck load.
The wall between the driveway and the roof needs insulation
A house perimeter of 140 linear feet at 8 ft ceiling height gives you 1,120 square feet of wall cavity. Subtract about 120 square feet for windows and doors and you have roughly 1,000 square feet to fill. The question is with what.
| Material | R-value per inch | Cost per sq ft | 1,000 sq ft total |
|---|---|---|---|
| Fiberglass batts | R-3.2 | $1.20-1.80 | $1,200-1,800 |
| Mineral wool | R-3.7 | $2.00-2.50 | $2,000-2,500 |
| Spray foam | R-6.0 | $3.00-5.00 | $3,000-5,000 |
Fiberglass at R-13 fills a 2x4 wall cavity for about $1.70 per square foot installed. Spray foam at R-24 in the same 4 inches costs $4+ but doubles as a vapor barrier. Three times the price, twice the R-value, plus air sealing. Whether that trade-off makes sense depends on your climate zone and how long you plan to own the house.
The insulation calculator subtracts windows and doors automatically, adds your waste margin and shows package counts for whichever material you pick. Plug in local prices and the total appears before you load the truck.
60 bundles of shingles - and that is just the covering
Roofing math starts with one number: the roofing square. One square equals 100 square feet. A 1,980 sq ft gable roof is 19.8 squares. Three bundles per square. That is 60 bundles of shingles stacked on your driveway waiting to go up.
But shingles are only part of the bill.
| Item | Quantity | Cost |
|---|---|---|
| Asphalt shingles | 60 bundles | $7,920 |
| Underlayment | 5 rolls | $792 |
| Ridge cap | ~50 linear ft | (included) |
| Labor (tear-off + install) | 1,980 sq ft | $5,940 |
| Total installed | $14,652 |
Metal panels would cut the bundle count (33 panels instead of 60 bundles) but push the installed price to $18,000+. Clay tiles? Over $25,000 - and you need a structural engineer to confirm the trusses can hold the weight. The roof calculator runs the numbers for all four material types.
The verdict: where does the money actually go?
For an average house with a two-car driveway, standard wall insulation and a new roof, the construction material breakdown looks roughly like this:
| Job | Materials | Labor | Total |
|---|---|---|---|
| Driveway (20x18 ft, 5 in) | $538 | $397 | $936 |
| Wall insulation (1,000 sq ft) | $700 | $1,000 | $1,700 |
| Roof (1,980 sq ft gable) | $8,712 | $5,940 | $14,652 |
| Combined | $9,950 | $7,337 | $17,288 |
The roof eats 85% of the total. A driveway - the thing you see and use every day - is barely 5% of the combined bill. Insulation sits somewhere in between, invisible inside the walls, quietly cutting your heating bill for the next 30 years.
Run your own numbers. The three calculators below take specific dimensions, local prices and your chosen materials - and return a bill of quantities before anyone shows up with a truck.
Concrete by slab thickness - quick reference
Pick your thickness and get pre-filled results:
4 in (sidewalks, patios) | 5 in (garage floors) | 6 in (driveways) | 8 in (post footings) | 10 in (heavy loads) | 12 in (strip footings)
Tools discussed in this article
Concrete Calculator - enter slab length, width and thickness. Get volume in cubic yards, cement bags, sand and gravel in tons, plus a cost estimate for three mix strengths.
Insulation Calculator - pick fiberglass, mineral wool, rigid foam or spray foam. Enter wall or attic dimensions, subtract openings, and get area, package count, R-value and cost.
Roof Calculator - measure slope length and width, pick shingles, metal, tiles or roll roofing. Get total area in squares, piece count, underlayment rolls and cost breakdown.
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Tile Calculator - count tiles, adhesive bags and grout packs for bathrooms and kitchens.
Paving Stone Calculator - plan pavers, base material and edging for driveways and patios.
Plaster Calculator - estimate plaster, stucco or drywall compound for walls and ceilings.