How High is Your Church Tower?

And how we calculated the height of Cockshutt Church tower!

The tower is one of the salient external features of many churches.  The tall structure greatly assists with pinpointing the precise location of a church and the tower bells allow the church to call parishioners to worship.  The church tower has served many additional purposes over the years, from providing sanctuary in times of upheaval to housing the pendulum weights for the mechanical clock on the face of the tower.

Figure 1: Schematic diagram of a church tower with a shadow

Upon seeing a church tower, it is natural to wonder how tall the structure is. We were unable to find any record of the height of Cockshutt church tower so, on a sunny summer bank holiday, we decided to measure it ourselves. The approach we used is an ancient method (which we call ‘Method 1’) for measuring tall structures. It involves measuring the length of the shadow of an object of known height (in our case, a wooden stake that was approximately 1 metre in length) and calculating the aspect ratio (defined in Figure 1) between the height of the object and the length of its shadow. This aspect ratio has a constant value for all objects at a particular time in the day.  We measured the length of Cockshutt church tower’s shadow and combined the measurement and aspect ratio to estimate the height of the tower to be 15.4 m.  More details regarding Method 1 can be found at  How can you measure the height of a tall tower? HowStuffWorks.

In order to cross-check our result, we used two additional methods (Method 2 and Method 3). You can read more about these below. Why not have a go at measuring the height of your own church tower? We would love to know how you get on!

BB 1647

We now give details of two additional methods that you can use to estimate the height of your church tower.

  • Method 2: This approach makes use of a photograph of the church tower (an example is given in Figure 2 (left)), in which the tower is approximately perpendicular to the principal axis of the camera.  When this constraint is satisfied, the ratio of object height and image height can be easily inferred directly from the image.  It is also necessary that the image contain a reference object of known height.  In our case, this object was the tower door, with height 2.4 m.  By printing off this image onto A4 paper and measuring the height of the door’s image with a ruler, we established the ratio between object height and image height and combined this with a measurement of the height of the tower’s image to arrive at an estimate of 15.2 m for Cockshutt church tower’s height.
  • Method 3: This approach makes use of a separate image of the tower and a measurement of the height of one row of bricks (in our case, 7.5 cm), which we assume to be approximately equal for all rows.  By counting the number of rows of bricks (using the image) and combining this value with the measured height of a brick row, we estimated Cockshutt church tower’s height to be 18.8 m. Our working is given in Figure 2 (right).
Figure 2: (left) Example image used for implementing method 2, (right) example image (with working) used for implementing method 3.

The first and second methods were in close agreement, so we concluded that the height of the church tower is approximately 15.4 m. We believe that there is significant error in our estimate using Method 3 primarily because the assumption of a constant brick-row height is inaccurate.

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