Calculadora de Laje
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
V = área × esp; aço ≈ 8 kg/m² (para 10 cm) × fator espessura
About this calculator
The Slab Calculator is a practical tool for estimating the volume of concrete and steel needed for solid reinforced concrete slabs. It is ideal for small to medium residential projects, helping engineers, architects, and self-builders plan materials more accurately.
The concrete volume is calculated by multiplying the slab area (in square meters) by the thickness (in meters). For example, a 50 m² slab with 10 cm thickness yields 5 m³ of concrete. The steel estimate uses an average consumption of 8 kg/m² for 10 cm slabs, adjusted proportionally for other thicknesses. This value is an initial reference, as the actual steel quantity depends on structural detailing and applied loads.
Use this calculator in the early project phases, such as material budgeting or comparing construction alternatives. It provides a basis for supplier negotiation and construction logistics planning. Remember that results are approximate and must be validated by a complete structural design, especially for slabs with large spans, high loads, or irregular geometries.
Important considerations: the steel estimate of 8 kg/m² is valid for conventional solid slabs with 10 cm thickness. For different thicknesses, the adjustment factor is linear (e.g., 12 cm → 9.6 kg/m²). However, this method does not replace structural design, which considers positive and negative reinforcement, minimum steel ratios, and details like openings. Always consult a civil engineer for final design.
Frequently asked questions
How accurate is the steel estimate from the calculator?
The estimate of 8 kg/m² for 10 cm slabs is an average for residential projects. Accuracy depends on structural detailing; for a more precise value, an engineering design is required.
Can I use this calculator for precast or ribbed slabs?
No. This calculator is specific for solid reinforced concrete slabs. Precast or ribbed slabs have different steel and concrete consumption.
How do I adjust steel quantity for thicknesses other than 10 cm?
Multiply 8 kg/m² by the actual thickness in cm divided by 10. Example: for 12 cm, use 8 × 1.2 = 9.6 kg/m². This adjustment is linear and approximate.
Does the calculator account for material waste?
No. It is recommended to add 5% to 10% margin for waste in concrete and steel, according to construction practices.
Do I need an engineer even if I use this calculator?
Yes. The calculator is a pre-sizing tool. The structural design must be done by a civil engineer to ensure safety and compliance with standards.