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Slab Load Calculator

Work out slab load instantly with clear inputs, formula shown and shareable results.

About Slab Load Calculator

Slab dead load starts with its own weight, thickness in metres times 25 kN/m³ for reinforced concrete, then adds screed, finishes and services. Live load comes from the occupancy schedule. The factored total drives design, and for a simply supported one-way slab the moment per metre width is wL²/8.

Formulas

Dead load

kPa = thickness m x 25 + finishes and services

Design moment

M = 1.2 dead + 1.6 live, then w L² / 8 per metre width

Worked example

With the default values below, Slab Load Calculator returns Total service load of 8.25. Change any input above and every figure here is recalculated in your browser.

Inputs used

Slab thicknessminimum 25 mm
150 mm
Finishes and servicesminimum 0 kPa
1.5 kPa
Live loadminimum 0 kPa
3 kPa
Effective spanminimum 0.1 m
4 m

Results

Total service load
8.25 kPa
Total dead load
5.25 kPa
Factored design load
11.10 kPa
Design moment per metre width
22.20 kN·m/m

Step by step

  1. 1Values used
  2. 2Dead load
  3. 3Design moment
  4. 4Total service load= 8.25 kPa
  5. 5Total dead load= 5.25 kPa
  6. 6Factored design load= 11.10 kPa
  7. 7Design moment per metre width= 22.20 kN·m/m

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or compounding frequency into account.
  • Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
  • Preliminary estimate only. Slab loads, spans and reinforcement must be designed by a qualified structural engineer to the applicable code.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Slab loads, spans and reinforcement must be designed by a qualified structural engineer to the applicable code.

Frequently Asked Questions

How is the Slab Load figure worked out?

kPa = thickness m x 25 + finishes and services. Slab dead load starts with its own weight, thickness in metres times 25 kN/m³ for reinforced concrete, then adds screed, finishes and services.

Why 25 kN/m³ for concrete?

Plain concrete is about 24 kN/m³ and reinforcement raises it to roughly 25. Codes specify 25 for normal weight reinforced concrete so the figure is consistent between designers.

What values do I need to enter?

This calculator takes 4 inputs: Slab thickness, Finishes and services, Live load, Effective span. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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Slab Load Calculator – Calculate Total service load