{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"concrete-slab"},"result":{"entity_type":"calculator","id":"concrete-slab","calculator_id":"concrete-slab","canonical_url":"https://tttkmbb.com/construction/concrete-slab","name":"Concrete Slab Calculator","title":"Concrete Slab Calculator – Volume in m³ and Cubic Yards, Bags of Premix (80 lb, 60 lb, 25 kg)","category":"construction","category_name":"Construction & Home","tool_name":"estimate_concrete_slab","featured_mcp_tool":false,"description":"Computes the concrete volume of a rectangular slab, footing or pad from length, width and thickness, adds a waste allowance and converts it to cubic yards, cubic feet and the number of 80 lb, 60 lb and 25 kg bags of premixed concrete.","use_when":"You need the amount of ready-mix concrete to order or the number of premix bags for a slab, patio, shed base, footing or pad of uniform thickness.","do_not_use_when":"The pour is a cylinder such as a post hole or pier (use cylinder for the volume), or you need mortar for brickwork (use brick).","inputs":[{"name":"unit_system","label":"Unit system","type":"enum","required":false,"default":"metric","values":[{"value":"metric","label":"Metric (m, cm, mm, m²)","aliases":["si","metres","meters"]},{"value":"imperial","label":"Imperial / US customary (ft, in, ft²)","aliases":["us","feet","inches"]}],"description":"Unit system of the length inputs (metric: m / cm / mm; imperial: ft / in). Outputs are reported in both systems.","example":"metric"},{"name":"length","label":"Slab length","type":"number","unit":"m or ft","required":true,"max":1000,"exclusive_min":0,"description":"Slab length in metres or feet.","example":4},{"name":"width","label":"Slab width","type":"number","unit":"m or ft","required":true,"max":1000,"exclusive_min":0,"description":"Slab width in metres or feet.","example":3},{"name":"thickness","label":"Slab thickness","type":"number","unit":"cm or in","required":true,"max":500,"exclusive_min":0,"description":"Slab thickness in centimetres (metric) or inches (imperial). Typical: 10 cm / 4 in for paths and patios, 15 cm / 6 in for driveways.","example":10},{"name":"waste_percent","label":"Waste allowance","type":"number","unit":"%","required":false,"default":10,"min":0,"max":50,"description":"Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). Covers uneven sub-base, spillage and over-excavation; 5–10 % is usual.","example":10}],"outputs":[{"name":"volume_m3","label":"Volume","type":"number","unit":"m³","decimals":3,"description":"length × width × thickness, before waste."},{"name":"volume_cubic_feet","label":"Volume","type":"number","unit":"ft³","decimals":2,"description":"Same volume in cubic feet."},{"name":"volume_cubic_yards","label":"Volume","type":"number","unit":"yd³","decimals":3,"description":"Same volume in cubic yards (1 yd³ = 27 ft³ = 0.7646 m³)."},{"name":"volume_with_waste_m3","label":"Volume to order","type":"number","unit":"m³","decimals":3,"description":"Volume × (1 + waste_percent/100)."},{"name":"volume_with_waste_cubic_yards","label":"Volume to order","type":"number","unit":"yd³","decimals":3,"description":"Volume to order in cubic yards."},{"name":"bags_80lb","label":"80 lb bags","type":"integer","decimals":4,"description":"ceil(volume_with_waste_ft³ / 0.60 ft³ per bag)."},{"name":"bags_60lb","label":"60 lb bags","type":"integer","decimals":4,"description":"ceil(volume_with_waste_ft³ / 0.45 ft³ per bag)."},{"name":"bags_25kg","label":"25 kg bags","type":"integer","decimals":4,"description":"ceil(volume_with_waste_m³ × 96 bags per m³), assuming about 2400 kg of dry premix per m³ of placed concrete."}],"input_schema":{"type":"object","properties":{"unit_system":{"description":"Unit system of the length inputs (metric: m / cm / mm; imperial: ft / in). Outputs are reported in both systems.","type":"string","enum":["metric","imperial"],"default":"metric","examples":["metric"]},"length":{"description":"Slab length in metres or feet. Unit: m or ft.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[4],"x-unit":"m or ft"},"width":{"description":"Slab width in metres or feet. Unit: m or ft.","type":"number","maximum":1000,"exclusiveMinimum":0,"examples":[3],"x-unit":"m or ft"},"thickness":{"description":"Slab thickness in centimetres (metric) or inches (imperial). Typical: 10 cm / 4 in for paths and patios, 15 cm / 6 in for driveways. Unit: cm or in.","type":"number","maximum":500,"exclusiveMinimum":0,"examples":[10],"x-unit":"cm or in"},"waste_percent":{"description":"Extra material for cuts, breakage and offcuts, applied as a multiplier (1 + waste_percent/100). Covers uneven sub-base, spillage and over-excavation; 5–10 % is usual. Unit: %.","type":"number","minimum":0,"maximum":50,"default":10,"examples":[10],"x-unit":"%"}},"additionalProperties":false,"required":["length","width","thickness"]},"output_schema":{"type":"object","properties":{"volume_m3":{"description":"length × width × thickness, before waste. Unit: m³.","type":"number","x-unit":"m³"},"volume_cubic_feet":{"description":"Same volume in cubic feet. Unit: ft³.","type":"number","x-unit":"ft³"},"volume_cubic_yards":{"description":"Same volume in cubic yards (1 yd³ = 27 ft³ = 0.7646 m³). Unit: yd³.","type":"number","x-unit":"yd³"},"volume_with_waste_m3":{"description":"Volume × (1 + waste_percent/100). Unit: m³.","type":"number","x-unit":"m³"},"volume_with_waste_cubic_yards":{"description":"Volume to order in cubic yards. Unit: yd³.","type":"number","x-unit":"yd³"},"bags_80lb":{"description":"ceil(volume_with_waste_ft³ / 0.60 ft³ per bag).","type":"integer"},"bags_60lb":{"description":"ceil(volume_with_waste_ft³ / 0.45 ft³ per bag).","type":"integer"},"bags_25kg":{"description":"ceil(volume_with_waste_m³ × 96 bags per m³), assuming about 2400 kg of dry premix per m³ of placed concrete.","type":"integer"}}},"formula":"volume = length × width × thickness (thickness/100 in m or thickness/12 in ft); with_waste = volume × (1 + waste_percent/100); yd³ = ft³ / 27; m³ = ft³ × 0.028316847; bags_80lb = ceil(ft³ / 0.60); bags_60lb = ceil(ft³ / 0.45); bags_25kg = ceil(m³ × 96).","method":"Bag yields follow the QUIKRETE data sheet (80 lb → 0.60 ft³, 60 lb → 0.45 ft³). The 25 kg count assumes ≈ 2400 kg of dry mix per m³ (96 bags), a conservative figure: manufacturer yields of 0.010–0.0125 m³ per 25 kg bag correspond to 80–100 bags/m³, so check the bag.","sources":[{"name":"QUIKRETE Concrete Mix No. 1101 product data sheet (yield: 80 lb bag 0.60 ft³, 60 lb bag 0.45 ft³)","url":"https://www.quikrete.com/pdfs/data_sheet-concrete%20mix%201101.pdf","type":"reference","retrieved_at":"2026-09-23"},{"name":"QUIKRETE – Concrete, mortar and post-setting calculators","url":"https://www.quikrete.com/calculator/main.asp","type":"reference","retrieved_at":"2026-09-23"},{"name":"Wikipedia – Concrete (density of normal-weight concrete ≈ 2400 kg/m³)","url":"https://en.wikipedia.org/wiki/Concrete","type":"reference","retrieved_at":"2026-09-23"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"10 ft × 20 ft slab, 4 in thick, 10 % waste","inputs":{"unit_system":"imperial","length":10,"width":20,"thickness":4,"waste_percent":10},"expected":{"volume_cubic_feet":66.67,"volume_cubic_yards":2.469,"volume_m3":1.888,"volume_with_waste_cubic_yards":2.716,"volume_with_waste_m3":2.077,"bags_80lb":123,"bags_60lb":163,"bags_25kg":200},"url":"https://tttkmbb.com/api/v1/calculate/concrete-slab?unit_system=imperial&length=10&width=20&thickness=4&waste_percent=10"},{"name":"4 m × 3 m slab, 10 cm thick, 10 % waste","inputs":{"unit_system":"metric","length":4,"width":3,"thickness":10,"waste_percent":10},"expected":{"volume_m3":1.2,"volume_cubic_yards":1.57,"volume_with_waste_m3":1.32,"volume_with_waste_cubic_yards":1.727,"bags_25kg":127,"bags_80lb":78,"bags_60lb":104},"url":"https://tttkmbb.com/api/v1/calculate/concrete-slab?unit_system=metric&length=4&width=3&thickness=10&waste_percent=10"}],"faq":[{"q":"Should I order ready-mix or use bags?","a":"Bags are practical up to roughly 0.5 m³ (about 30 × 80 lb bags); above that, ready-mix delivered by truck is cheaper and gives a consistent mix. Ready-mix is ordered by the m³ or yd³ using the with-waste figure."},{"q":"Why do bag counts differ between brands?","a":"Yield per bag depends on the mix design and how much water is added; the figures here are QUIKRETE's for US bags and a conservative 2400 kg/m³ assumption for 25 kg bags. Use the yield printed on the bag when it differs."}],"tags":["concrete calculator","cubic yards of concrete","concrete slab","bags of concrete","premix bags","m3 of concrete"],"related":[{"calculator_id":"gravel","reason":"Sub-base aggregate under the slab."},{"calculator_id":"brick","reason":"Bricks and mortar for walls on the slab."},{"calculator_id":"cylinder","reason":"Volume of round post holes or piers."}],"links":{"html":"https://tttkmbb.com/construction/concrete-slab","markdown":"https://tttkmbb.com/construction/concrete-slab.md","json":"https://tttkmbb.com/construction/concrete-slab.json","api":"https://tttkmbb.com/api/v1/calculate/concrete-slab","schema":"https://tttkmbb.com/api/v1/calculators/concrete-slab","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-23"},"timestamp":"2026-09-23T23:32:04Z","next_actions":[{"tool":"run_calculator","calculator_id":"concrete-slab","reason":"Run Concrete Slab Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/construction/concrete-slab.md"}}