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Scaffold Load Calculator

Scaffold Load Calculator: Platform Area, kN/m² and Load Classes Explained

Scaffold loading starts with simple arithmetic: platform area multiplied by a uniform load. Learn how to calculate boarded area and total imposed load, what the BS EN 12811 load classes mean, and why this is never a substitute for TG20 or a competent person’s design, with worked examples and a free educational calculator.

Last updated 7 November 2026

Important: this is for learning, not design

This guide and the calculator it links to are educational. They show the basic arithmetic of platform area and uniformly distributed load. They do not design a scaffold, check it against TG20 or manufacturer data, or confirm that any scaffold can carry any load. Scaffold design, inspection and handover must be done by a competent person, and non-standard scaffolds need a competent designer or temporary works engineer.

With that clear, understanding the maths helps site teams read a scaffold’s load class, talk about loading sensibly and spot when something does not add up.

The basic idea

A boarded scaffold platform is rated for a service load spread evenly over its area. That uniformly distributed load is measured in kilonewtons per square metre (kN/m²). To see what a rating means in total, you multiply it by the platform area. KaelSite’s free Scaffold Load Calculator does that arithmetic in three ways: from a load class, from a load per m², or from a total applied load.

The formulas

  • Platform area (m²) = boarded length × boarded width
  • Total boarded area = area per platform × number of identical platforms
  • Total imposed load (kN) = load per m² × total boarded area
  • Load per m² (kN/m²) = total applied load ÷ total boarded area
  • Approximate kg-force = kN × 1,000 ÷ 9.81

The kg-force figure is only a rough way to express the load in kilograms, because site teams often talk about the weight of materials. It is an illustration of the uniform load you entered, not a capacity check.

BS EN 12811 service load classes

BS EN 12811-1 sets out service load classes for working scaffolds. The calculator shows these as guide figures:

Class Uniform load Approx. kg-force per m²
Class 1 0.75 kN/m² 76
Class 2 1.50 kN/m² 153
Class 3 2.00 kN/m² 204
Class 4 3.00 kN/m² 306
Class 5 4.50 kN/m² 459
Class 6 6.00 kN/m² 612

 

Higher classes are for heavier duty. Selecting a class in the calculator only shows the arithmetic for that pressure. It does not mean your scaffold is that class. Refer to TG20 and your scaffold designer for what each class is used for and what the scaffold is actually designed for.

Worked examples

These examples show arithmetic only. They are not checks of real scaffolds.

1. One platform at a class pressure
A boarded platform 6 m long and 0.9 m wide:
Area = 6 × 0.9 = 5.4 m²
At 2.00 kN/m²: 5.4 × 2.00 = 10.8 kN
Approximate kg-force: 10.8 × 1,000 ÷ 9.81 = about 1,100 kgf

2. Several identical platforms
Three identical platforms, each 8 m × 1.2 m:
Area per platform = 8 × 1.2 = 9.6 m²
Total area = 9.6 × 3 = 28.8 m²
At 1.50 kN/m²: 28.8 × 1.50 = 43.2 kN
Approximate kg-force: about 4,400 kgf
Real scaffolds often have different widths and loadings on each lift, and that needs proper design.

3. Working backwards from a total load
A total of 6 kN applied over a platform 4 m × 1.0 m:
Area = 4 m²
Load per m² = 6 ÷ 4 = 1.5 kN/m²
That equals the Class 2 figure, but arithmetic alone does not make a scaffold Class 2.

What the calculation does not cover

The simple area × load model leaves out most of what matters in practice:

  • Concentrated loads, such as a stack of materials in one spot
  • Partial boarding and uneven loading
  • Dynamic effects, such as dropped materials or impact
  • Ties, standards, ledgers, transoms and boards
  • Foundations and ground conditions
  • Wind and sheeting or netting

These are why scaffold design uses recognised guidance and, where needed, engineering calculations.

Common mistakes

  • Treating a load class as proof of capacity. A class is a design and use category, not something you can assign by calculation.
  • Assuming all lifts are loaded the same. Real scaffolds are rarely identical on every lift.
  • Ignoring stored materials. Heavy materials stacked on a platform can exceed the intended duty quickly.
  • Mixing units. Entering millimetres as metres makes the area wrong by a factor of a million.
  • Confusing kN and kg. One kilonewton is roughly 102 kg of force.
  • Using the calculator to justify a change. Altering a scaffold or its loading needs the scaffold designer or competent person.

UK rules and guidance

In Great Britain, scaffolding work falls under the Work at Height Regulations 2005, which require work to be planned, carried out safely and by competent people, and require scaffolds to be inspected before first use and at regular intervals. NASC TG20 is the recognised guide for standard tube and fitting scaffolds, and BS EN 12811 covers performance requirements and design of temporary works equipment. Anything outside a standard compliant configuration needs a competent designer. Scaffolds also sit within your wider temporary works procedures: see our guides to BS 5975 and temporary works procedures and temporary works management.

Frequently asked questions

Is this a scaffold design calculator?
No. It is an educational tool that multiplies platform area by a uniform load. It does not design or check scaffolds.

How do I calculate platform area?
Multiply boarded length by boarded width. For several identical platforms, multiply by the number of platforms.

What are BS EN 12811 service load classes?
Guide uniform loads from Class 1 (0.75 kN/m²) to Class 6 (6.00 kN/m²). Picking one in the calculator only shows the arithmetic.

How is total imposed load calculated?
Load per m² multiplied by total boarded area. Working backwards, load per m² is the total load divided by the area.

Can I use this instead of TG20 or a temporary works engineer?
No. Follow TG20 or the relevant system guidance and use a competent designer where the scaffold is not a standard configuration.

Why show an approximate kg-force figure?
It converts kilonewtons to a rough weight in kilograms, which is how site teams often think about materials. It is not a capacity check.

Related calculators

For site quantities and planning around scaffolded work (not scaffold design), these tools may help:

See all of them in our complete guide to free construction calculators.

Keep your scaffold records in one place

Scaffold inspections, handover records and photos need to be kept and easy to find. KaelSite helps UK site teams manage inspections, safety and reporting from one mobile-first app. Explore KaelSite features.

References