How much concrete for a 18×18 slab 5 inches thick?
Answer
5.00 cubic yards
188 bags of 80lb concrete mix300 bags of 60lb mixOrder ready-mix delivery (~$750)Add 10% for waste = 5.50 cy
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How We Calculated This
Cubic yards = (L × W × D/12) / 27
(18 × 18 × 5/12) / 27 = 135.00 / 27 = 5.00 cubic yards
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Calculated using verified formulas. Last updated March 2026.