What is Spirit Level? | How To Use Bubble Levels

What is Spirit Level?

A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb). Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights, and other metalworkers, and in some photographic or video graphic work.

A Spirit Level is a tool used to indicate how parallel (level) or perpendicular (plumb) a surface is relative to the earth. A spirit level gets its name from the mineral spirit solution inside the levels. The best spirit level is accurate to within plus or minus 0.5 millimeters/meter, or 0.005 inches/inch or 0.029 degrees.

Typically, the vials in a spirit level are a yellowish-green color with additives for UV protection and maximum performance in temperatures ranging from -20 degrees F to 130 degrees F.

The next level of accuracy displayed is 0.75mm/m or.043 degrees. The vial bodies of a spirit level, also referred to as a bubble level, can be shaped like a barrel, like a rectangular block, or even curved, banana-shaped, to measure slope infractions per foot of pitch; and are mostly made from acrylic today versus glass originally.

A spirit level, bubble level, or simply a level, is an instrument designed to indicate whether a surface is horizontal (level) or vertical (plumb).

Construction

Early tubular spirit levels had very slightly curved glass vials with a constant inner diameter at each viewing point. These vials are incompletely filled with a liquid, usually a colored spirit or alcohol, leaving a bubble in the tube.

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They have a slight upward curve so that the bubble naturally rests in the center, the highest point. At slight inclinations, the bubble travels away from the marked center position. Where a spirit level must also be usable upside-down or on its side, the curved constant-diameter tube is replaced by an uncurved barrel-shaped tube with a slightly larger diameter in its middle.

Alcohols such as ethanol are often used rather than water. Alcohols have low viscosity and surface tension, which allows the bubble to travel the tube quickly and settle accurately with minimal interference from the glass surface.

Alcohols also have a much wider liquid temperature range, and will not break the vial as water could due to ice expansion. A colorant such as a fluorescein, typically yellow or green, may be added to increase the visibility of the bubble.

A variant of the linear spirit level is the bull’s eye level: a circular, flat-bottomed device with the liquid under a slightly convex glass face with a circle at the center. It serves to level a surface across a plane, while the tubular level only does so in the direction of the tube.

Calibration

To check the accuracy of a carpenter’s type level, a perfectly horizontal surface is not needed. The level is placed on a flat and roughly level surface and the reading on the bubble tube is noted. This reading indicates to what extent the surface is parallel to the horizontal plane, according to the level, which at this stage is of unknown accuracy.

The spirit level is then rotated through 180 degrees in the horizontal plane, and another reading is noted. If the level is accurate, it will indicate the same orientation with respect to the horizontal plane. A difference implies that the level is inaccurate.

Adjustment of the spirit level is performed by successively rotating the level and moving the bubble tube within its housing to take up roughly half of the discrepancy until the magnitude of the reading remains constant when the level is flipped.

A similar procedure is applied to more sophisticated instruments such as a surveyor’s optical level or a theodolite and is a matter, of course, each time the instrument is set up. In this latter case, the plane of rotation of the instrument is leveled, along with the spirit level. This is done in two horizontal perpendicular directions.

How to Check a Spirit Level for Accuracy

  • Place the level on a flat surface.
  • Make one mark at the end of the level.
  • Make another mark along the side of the level, under the vial in the center.
  • Take a reading of the bubble’s position.
  • Rotate the level 180° end-to-end and align the level with your marks.
  • Take another reading. If the level is accurate, the bubble will be in the same position for both readings.
  • To test the vertical vial, follow the same procedure against a flat vertical surface.

How to Read a Spirit Level

  • Locate the bottom edge of the level. This rests against the surface you’re trying to level.
  • Some models feature magnetic edges, which “stick” to metal surfaces for ease of use.
  • Inspect the body of the level and check for grabbing points where you won’t block the vials with your hand(s).
  • Most levels feature a punched hole on at least one end for hanging above your workbench.
  • The tube vial in the center of the level helps you find the true horizontal.
  • Tube vials on the ends finds the true vertical.
  • On many torpedo levels and other specialized levels, there is an angled tube vial to find level at 45°.

How to Use a Spirit Level

  • Clean the level, removing all buildup and dirt from the edges.
  • Mark a line along the bottom edge on the wall.
  • Flip the level over so that the bottom becomes the top. Put the new top edge along the marked line. If the bubble is centered, your level is accurate. If not, it is defective.
  • Place the level on the surface of the object for which you want to find the true horizontal (the “horizon”). Make sure the spirit tube runs parallel to the object. Allow the bubble to float to the top of the spirit tube.
  • Put your eyes at level with the spirit tube. In order to get an accurate reading, close one eye.
  • Take note of where the bubble is inside the spirit tube. If it’s centered between the lines on the tube, your object is level. If the bubble is to the right of the lines, your object slopes downward right-to-left. If the bubble is to the left of the lines, your object slopes downward left-to-right.
  • To find the true vertical or “plumb,” repeat the same process vertically.

How to Level a Scope with a Bubble Level

  • Ensure your rifle is unloaded.
  • Place the rifle in a vise, gun cradle, or any other holder keeping the rifle secure.
  • Place a bubble level on a flat part of the gun. If you have a second spirit level, use it on another flat part, such as the action, above the chamber or on the rib.
  • Tighten the rifle in place when you reach level.
  • Place the scope in the rings.
  • Tighten the scope snug, but loose enough to be able to shift it slightly.
  • Place a bubble level on the scope and level the scope horizontally.
  • Rotate the level parallel to the scope and level it vertically.
  • Your scope is now level.

Types of Spirit Levels

There are different types of spirit levels for different uses:

  • Surveyor’s leveling instrument
  • Carpenter’s level (either wood, aluminum or composite materials)
  • Mason’s level
  • Torpedo level
  • Post level
  • Line level
  • Engineer’s precision level
  • Electronic level
  • Inclinometer
  • Slip or Skid Indicator
  • Bull’s eye level

A spirit level is usually found on the head of combination squares.

1. Surveyor’s leveling instrument

‘Tilting level’, dumpy level or ‘automatic level’ are terms used to refer to types of ‘leveling instruments’ as used in surveying to measure height differences over larger distances. A surveyor’s leveling instrument has a spirit level mounted on a telescope (perhaps 30 power) with cross-hairs, itself mounted on a tripod.

The observer reads height values off two graduated vertical rods, one ‘behind’ and one ‘in front, to obtain the height difference between the ground points on which the rods are resting.

Starting from a point with a known elevation and going cross country (successive points being perhaps 100 meters (328 ft) apart) height differences can be measured cumulatively over long distances and elevations can be calculated. Precise leveling is supposed to give the difference in elevation between two points one kilometer (0.62 miles) apart correct to within a few millimeters.

2. Carpenter’s level

A traditional carpenter’s spirit level looks like a short plank of wood and often has a wide-body to ensure stability, and that the surface is being measured correctly. In the middle of the spirit level is a small window where the bubble and the tube are mounted.

Two notches (or rings) designate where the bubble should be if the surface is level. Often an indicator for a 45-degree inclination is included.

3. Line level

A line level is a level designed to hang on a builder’s string line. The body of the level incorporates small hooks to allow it to attach and hang from the string line. The body is lightweight, so as not to weigh down the string line, it is also small in size as the string line in effect becomes the body; when the level is hung in the center of the string, each ‘leg’ of the string line extends the level’s plane.

4. Engineer’s precision levels

An engineer’s precision level permits leveling items to greater accuracy than a plain spirit level. They are used to level the foundations, or beds of machines to ensure the machine can output workpieces to the accuracy pre-built in the machine.

How Spirit Levels are Made

Spirit levels are made from a variety of materials including aluminum, plastic, wood, cast iron, and composite materials. Users of spirit levels are categorized as professional contractors and tradesmen, such as carpenters, masons, framers, electricians, plumbers, and woodworkers; and do-it-yourselfers, such as a homeowner.