Concrete Slab Calculator — m, cm to m³, bags, cost
How to use this calculator
Pick a shape, type each dimension and choose the unit (m, cm, or mm) from the dropdown next to it. Thickness rule of thumb: 10 cm patios and paths, 12–15 cm driveways and garage slabs, 20 cm+ for heavy or vehicle-loaded pads. The slab is sized for the pour — sub-base, vapour barrier and edge thickening are separate items in a real takeoff, so toggle them on below when they belong in your scope.
Cost — pick ready-mix delivery per m³, 50 kg bags, or 25 kg bags. Select your currency (EUR, PLN, CZK, SEK, etc.) in the settings below.
Reinforcement — welded wire mesh per EN 10080 or rebar Ø8–Ø20 with spacing 100–300 mm per EN 1992-1-1 (Eurocode 2), including lap splices and concrete cover.
Labor — rate per m², per m³, or a flat price. Grand total sums all active sections.
Saved Calculations
| Time | Shape | Area m² | Vol m³ | Cost | Rebar | Qty | Rebar | Labor | Total |
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How to Calculate Concrete for a Slab (Metric)
Volume is area × thickness in metres. Pick the shape, enter dimensions in m, cm or mm, then set thickness: 100 mm for patios and footpaths, 120–150 mm for driveways, 200 mm+ for heavy-duty or trafficked slabs. Weight uses a concrete density of 2 400 kg/m³ and is shown in tonnes once it passes 1 000 kg. The truck minimum is typically 1 m³, so round small pours up.
Waste, bags vs. ready-mix
Use 5% waste for clean rectangular pours, 10% as the typical default, and 15–20% for L-shapes, pumped placement, or hand-dug edges. Bagged mix only makes sense below roughly 1 m³ — a 50 kg bag yields about 0.024 m³ and a 25 kg bag about 0.012 m³. Above that, ready-mix per cubic metre is cheaper and faster than mixing bags.
Reinforcement per EN 1992-1-1 (Eurocode 2)
Choose welded wire fabric (Q188, Q257 or Q335 per EN 10080) for crack control, or B500B bars Ø6–Ø20 at 100–300 mm centres for structural slabs. Lap splices use 40db per EN 1992-1-1 §8.7; concrete cover follows the exposure class (XC1–XC4, XD/XS per §4.4.1). Standard bar length is 6 m and fabric sheets are 2.4 m × 6 m (14.4 m²). Thickened edges and integral footings can be sized with the spread footing calculator or the strip footing calculator; isolated supports use the concrete pier calculator and turned-down beams the grade beam calculator.
On pour day
Three line items estimators forget. Short-load fee — most batching plants charge €60–120 on orders under ~3 m³, so a 3.6×3.6 m patio (≈1.3 m³ at 10 cm) often comes out cheaper in 25/50 kg bags. Thickened edge — monolithic shed and garage slabs need a 200×200 mm haunch around the perimeter; add it as its own line, not as more "waste". Concrete pump — back-garden pours past 10 m of hose, first-floor decks, or anywhere a truck can't reverse need a boom or line pump (typically €450–900 minimum). C25/30 ready-mix in 2025 EU averages €110–160/m³ delivered with a 1 m³ minimum, and EN 1992-1-1 §9.2 requires control joints at roughly 24–36× slab thickness in each direction. Save runs to History and export text, CSV, A4 JPG, or PDF with the diagram — estimates are planning numbers, not a substitute for a structural drawing.
