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Sensitivity & Accuracy of Spirit Level Vials

Level Developments are experts in the manufacture of professional, highly sensitive and accurate levels, perfectly positioning us to give an overview of the term ‘sensitivity’ in relation to spirit levels, bubble levels and spirit level vials.


Sensitivity is an important specification for spirit levels and bubble vials as it plays a big part in determining the overall accuracy of the device. The sensitivity of a level or vial is defined as the change of angle or gradient required to move the bubble by a set distance (usually 2mm). If the vial has graduated divisions then the sensitivity refers to the angle or gradient change required to move the bubble by one of these divisions (often spaced at 2mm).


Due to the nature of angle-measuring devices and their applications, angles are often measured in units such as degrees, minutes and seconds. Use the table below to configure and convert between these units

Degrees° Minutes’ Seconds”


For all spirit levels, the sensitivity specification is determined by the sensitivity of the vials that are used. This is determined by the radius of curvature within the vials, which the bubble moves across. All spirit level vials and bubble vials contain this curved radius, even though it cannot always be seen. This allows the bubble to move to the highest point of the radius as gravity acts on the liquid inside the vial once it is level. The sensitivity is directly related to the radius of curvature of the vial:

  • The longer the radius, the more sensitive the vial will be
  • The shorter the radius, the coarser the vial will be

Use our table below or enter your own values to determine what radius you need for your desired sensitivity, per 2mm division.

Radius mm
Sensitivity per 2mm bubble movement
Deg °
Deg °
Min ’
Sec ’’
30 3.8200 3 49 12 66.62
60 1.9100 1 54 36 33.33
120 0.9550 0 57 18 16.67
240 0.4775 0 28 39 8.33
480 0.2388 0 14 20 4.17
960 0.1194 0 7 10 2.08
1920 0.0597 0 3 35 1.04
4000 0.0287 0 1 43 0.50
8000 0.0143 0 0 52 0.25
16000 0.0072 0 0 26 0.13
32000 0.0036 0 0 13 0.06
64000 0.0018 0 0 6 0.03
100000 0.0011 0 0 4 0.02

At Level Developments, we manufacture vials with radiuses from 30mm to 100 metres to suit a wide range of applications, where the sensitivity can be defined as an angle or a gradient. As an angle, the standard units are degrees (°), minutes (′) and seconds (″). 1 degree = 60 minutes and 1 minute = 60seconds. (1° = 60′ and 1′ = 60″). As an example, if we were to lift one end of a level vial by 5 degrees and the bubble moved by 2mm, this would give a sensitivity of 5°/2mm. We can also express this as a gradient where 5° = 87 mm/m (tan5° = 0.087m), meaning if a 1 metre beam was lifted on one end by 87mm or 5°, it would cause a 2mm movement of the bubble.

Spirit Level Bubble Vials

Deciding Which Sensitivity

Sensitivity is such an important specification as it allows the correct vial or spirit level to be used for specific applications. The way to determine the sensitivity required is to identify the maximum off-angle the application can allow while still operating as intended. The accuracy at which users can centre the bubble in the vial should also be considered, which is usually assumed to be 0.5mm. For example, if a product needs to be level within 0.1° (or 6’), a vial that will give at least 0.5mm bubble movement for a 0.1° (6’) change in angle will be required. This corresponds to 0.4° (24’) for a 2mm bubble movement, therefore a vial with a sensitivity of 24’/2mm (24 minutes per 2mm bubble movement) is needed.


We have a wide range of Sensor Vials, Bubble Levels, Circular Levels and Ground Vials that may be suitable for you, or contact us to identify the perfect vial and sensitivity for your application. Please email Level Developments or use our online contact form to get in touch.