How To Calculate & Measure Formwork

Author: Muriel

Dec. 16, 2024

How To Calculate & Measure Formwork

How to calculate formwork for columns

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Formwork is needed to support vertical concrete forms such as columns, pillars, posts, shafts, struts and walls.

For square or rectangular forms, calculate the perimeter of the base and multiply it by the height.

For round or elliptical columns, calculate the area by multiplying the circumference (2πr) by the height.

If you're making any home improvements involving concrete, you're going to need formwork to hold it in place while it hardens. Knowing how to calculate formwork will make sure you order enough materials and can budget your project more accurately.

Follow this guide to find out how to measure formwork you need. If you don't want to calculate formwork yourself, you can hire a professional formwork estimator to take care of it.

Find out more: What Is Formwork?

How to measure formwork

While you'll be ordering concrete by volume, formwork is measured by area. Specifically, the area that will actually be in contact with the concrete. This means calculations will be in square meters (or square millimetres if more accuracy is needed).

To measure the area of formwork needed to support your concrete installation, multiply the perimeter or circumference by the length/height of the structure. Each side of concrete will need its own formwork calculation and more complex or irregular shapes will have more complex calculations.

How to calculate formwork for slabs

If you're laying a concrete path, driveway, foundations or other base or flat surface, you only need to know how to calculate formwork area.

· For simple square and rectangular forms, simply multiply length x width to know how much formwork you need.

· For a circular base, multiply the square of the radius by pi (πr²).

· For irregular shapes, break these down into simpler squares and rectangles and add up the total surface area.

How to calculate formwork for columns, walls and posts

Formwork is needed to support vertical concrete forms such as columns, pillars, posts, shafts, struts and walls.

· For square or rectangular forms, calculate the perimeter of the base and multiply it by the height.

· For round or elliptical columns, calculate the area by multiplying the circumference (2πr) by the height.

If you're making formwork yourself, plywood supported by a lumber frame is the most economical option, but this won't be an option for round or irregularly shaped columns. These require metal formwork, which may need to be installed by a professional.

How to calculate formwork for beams and girders

Formwork for concrete beams, girders and other horizontal forms should only be fitted on three sides, with shuttering supporting the two vertical sides and the bottom face. The top face should be left exposed.

Add the lengths of the three sides, then multiply by the span of the beam to calculate the formwork area needed.

Square and rectangular beams and girders may be made from plywood supported by lumber or metal. Round formwork should be made from metal.

Formwork calculation example

For an example of how to calculate formwork for columns, let's say you need to estimate formwork for square concrete posts measuring 0.2m in length, 0.2m in width and 3.0m in height. The formwork uses plywood shuttering measuring 1.2m x 2.4m supported by a lumber frame.

To estimate how much plywood formwork you need to buy, you need to multiply the perimeter by the height to get the surface area needed for one column, then multiply this by the number of columns you need. Finally, you need to estimate how much plywood this would take.

Step 1: Calculate the concrete perimeter

Calculate the perimeter by adding the lengths of the four sides (a, b, c, d) and adding an extra 0.2m for overlapping of joints.

In this example, the calculation is:

 

Perimeter = a + b + c + d + 0.20

Perimeter = 0.2 + 0.2 + 0.2 + 0.2 + 0.2

Perimeter = 1.0m

 

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Step 2: Calculate the concrete surface area

Multiply the perimeter by the height of the column to get the surface area of the plywood shuttering.

 

Area = Perimeter x height

Area = 1.0 x 3.0

Area = 3.0m²

 

Step 3: Multiply by the number of columns

Let's say you're building 8 columns. The total area of all the concrete columns will be:

 

Total area = Area x number of columns

Total area = 3.0 x 8

Total area = 24m²

 

Step 4: Calculate the plywood surface area

Calculate the surface area of the size of plywood you're using. This example uses 1.2m x 2.4m plywood.

 

Plywood area = length x width

Plywood area = 1.2 x 2.4

Plywood area = 2.88m²

 

Step 5: Calculate how much plywood is needed

Divide the total concrete surface area by the surface area of one piece of plywood. This tells you how much plywood you need to buy.

 

Plywood needed = Total area / Plywood area

Plywood needed = 24 / 2.88

Plywood needed = 8.333

 

This means you'll need to buy 9 pieces of 1.2m x 2.4m plywood along with suitable falsework for support.

 

Common issues with formwork measurements

The difficulty of how to calculate formwork largely depends on the shape of the concrete form you're supporting. While a square or rectangular form will be straightforward to calculate and suitable for modular formwork, round or irregular forms may be more challenging and needs to be custom made.

If formwork can be reused on the same project or on future projects, this will lower the overall cost. However, the measurements need to be precisely the same each time. Metal formwork can be reused multiple times, but wooden formwork may not stand up to reuse, especially over long periods.


Find out more: How to Remove Formwork

how to calculate footings formwork?

How can we model formwork in order to calculate area for footings?

columns and walls ok, but what about footings, strip footing?

Contact us to discuss your requirements of ground beam formwork. Our experienced sales team can help you identify the options that best suit your needs.

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