Guide to Optical Levels

Reviewed by David Carmichael, Solution Engineer (October 2024)

An optical level – also known as a builder’s level, surveyor’s level, or dumpy level – is an optical instrument for measuring the height or levels of objects or marks on the same horizontal plane. Optical levels commonly come up in surveying and construction. They can be used for levelling and settlement determinations and in establishing the correct height of railways, pipelines, and roads. Optical levels are also used to accurately level machinery on the shopfloor.

 Read this guide to find out more about optical levels, how they work, and the best optical level for your application.

There are a number of different types of optical level. The oldest is the wye level, or ‘Y level,’ a bulky device that was invented in 1740 by Jonathan Sisson, an English inventor and instrument maker. This was superseded by the original dumpy level, developed by William Gavatt in 1830. The new technology was known as ‘dumpy’ because its telescope was short and fat. Despite evolutions in the design, the name persists to this day.

We’ve heard why it got its name, but what is a dumpy level? Today’s dumpy level (also often referred to as a ‘builder’s level’) is a common type of optical level instrument for taking measurements on the levelling staff. A dumpy level includes an eyepiece with a focus adjustment to focus on the staff. The dumpy level will also include a spirit level for horizontal alignment.

When you consider how to use a dumpy level, it’s crucial it is set up to be perfectly horizontal, which enables accurate measurements. The dumpy level is attached to an adjustable tripod. The tripod should be adjusted so that it provides a solid, level platform for the surveyor or builder.

And just what is an automatic level? Automatic optical levels (sometimes called a ‘builder’s auto level’) feature a mechanism that reduces variation in the set-up of the level so that even if the optical level is not perfectly horizontal, it will still give accurate measurements. The horizontal plane is established by a system of optical prisms and mirrors supported by wires (a bit like a pendulum). Builders and surveyors often favour automatic levels because of their speed to set up and use.

A tilting level is a modified dumpy level where the telescope is not fixed. Rather, the telescope can be vertically tilted.

A tilting level features a rotating knob. When the knob is rotated, the end of the telescope goes up or down, which changes the line of sight without having to adjust the tripod. The tilting level features two bubbles (known as a ‘split bubble’ design): one to level the instrument and another bubble to level the telescope. The split bubble means the surveyor is not entirely reliant on the accuracy of the levelling of the tripod, with the telescope’s bubble also helping to ensure it is level.

Optical level applications include construction, the building trade, and surveying. Let’s look at some of those optical level uses in more detail. 

Builders and construction companies use optical levels to determine the height of objects or marks onsite. This helps ensure that the final design is true to the plan. As well as being used on building and construction sites, the optical level is used by gardeners for landscaping.

Levelling is a process for measuring and marking elevation on a landscape or in the built environment, so for a surveyor, it’s a crucial part of the job. Optical levels are used by surveyors for this purpose. Much like a surveyor, farmers also use optical levels to measure points of elevation on their land.

Optical instruments come in a range of magnifications, while some designs are particularly ruggedised and robust for tough environments. Other optical levels feature easy-to-read displays or weather resistance. Automatic levels are renowned for being easier and quicker to set up, which is great when time is of the essence on a construction site. And the most durable optical levels will be good for everything from dusty, dirty sites to levelling production machinery at a manufacturer.

With so many types of optical level on the market, including the tried and tested dumpy level, tilting and automatic designs, and many others, you’re bound to be able to find the right optical level for your application.

Did you know that as well as dumpy levels, RS carries a wide range of displays and optoelectronics? Explore the products we offer today.