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How long is a piece of string?

Present students with a piece of string (4–5 metres) and discuss how to estimate its length. Show students how a standard informal measure can be used as a benchmark to estimate the length of the string.

Person holding a piece of material from outstretched hand to nose with head averted. Length of material marked as 1 metre.

Using an armspan to measure.


Watch the Armspan video which explains the process.


You can download the Armspan video transcript.


The body proportions of children and teenagers differ from those of adults. To compare, measure the arm span for each student in the class using the 1 metre benchmark method.

Use the data to draw a histogram to demonstrate the variation in the arm span measurement amongst the students.

Calculate the mean of the class data and compare it with the benchmark measurement for adults of 1 metre.

Use the average arm span length calculated from the class data to gain an estimate of the length of the string.

Measure the string using a tape measure and compare the estimate to the exact length of the string. 

Curriculum links

Year 7: Calculate mean, median, mode and range for sets of data. Interpret these statistics in the context of data

Year 8: Explore the variation of means and proportions of random samples drawn from the same population