Straight Edge Vs. Ruler

Wondering about the differences between straightedge and ruler? Indeed, both of them look like a long blade, but they are not the same. Are you confused about which one to use for your project? This page will cover the answers to those questions.


1. Function

A ruler is one of the most common and basic tools used to measure length. You can use it to measure the object’s dimensions be its length, width, and depth.

2. Accuracy of the Graduation

Due to its purpose for length measurement, the accuracy of the ruler graduation is highly important for a ruler to be considered a precision ruler. Again, it depends on the use. If you use it as desk ruler (to draw straight lines), the graduation accuracy may not that critical.

3. Models of Ruler

The ruler is available in different sizes and with different types of measurement marks on it depending on their application and is built using a variety of materials. On the basis of size, graduation, material, and their applications, there are several types of ruler including steel rulers, meter sticks, folding rulers, measuring tapes, seamstress tapes, and engineer rulers.

The most commonly used ruler type is a desk ruler (can be made from metal or plastic) which is used by students and engineers for drawing different shapes. It is made using wood or plastic or steel.

The measuring tape is the second most commonly used ruler type. It is mostly made of a metallic strip that is folded in a plastic enclosure. This tool is generally used in construction for measuring the dimensions of objects such as walls, etc. It serves you with graduations in inches, feet, cm, fractions, etc.

Don’t forget about the precision ruler (engineer rulers). It’s used by machinists, thus considered a machinist ruler. It serves you with greater accuracy compared to a desk ruler.

4. The Applications of Ruler

It is being used by students of different grades for their small level measurements and for drawings of geometrical features having straight lines. It is also being used by carpenters and construction workers for manufacturing of dimensionally accurate furniture and for the construction of different surfaces with desired dimensions. It is also used by machinists for the manufacturing of dimensionally accurate parts. Other than measurement, the ruler is also used where straight lines need to be drawn or for straight cutting of papers or similar materials.

5. Calibration of Ruler

To check the accuracy of your ruler, you need to compare it with the more accurate one. Put them side by side, by using the loupe, you can check the how the markings are aligned. The machinist rulers, in this case, will show you a neat marking and graduation lines.

Straight Edge

Straight edge is an important tool for straightness inspection. It is a long blade that by looking, it looks similar to a ruler. However, a typical straight edge commonly contains no graduation.

There are many products of rulers on the market that claim that they are straight edge. It’s not a straight edge unless comes with a straightness tolerance, which further is classified to a certain grade. Check out our selection of straight edges here. By reading this article, hopefully, you get the point and can differentiate them.

1. Function

Though some models have the same look as rulers, straightedge has a different purpose. The reason for using a straightedge is to check the straightness or flatness of a surface.

2. Models

You can find several models of the straightedge to choose from based on your need. One of the models has a sharp edge.

Typically, the straightedge are not used to measure the length because it doesn’t contain graduation or marking on it. However, some models have graduation as well. Similar to rulers whose main function is for length measurement, some rulers are made with tight straightness as well like the combination square (certain brand) whose blade has fine straightness.

3. The Applications of Straight Edge

A straightedge is used by architects, woodworkers, metalworkers, engineers and developers in different construction and industrial projects, where the sole reason for its usage is to make sure that different surfaces and lines are straight and do not contain any curves, breaks, or splines.

Since a typical straightedge does not have measurement markings (graduation) on its blade, so it cannot be used in places where measurement of length is required.

Aside from straightness, this tool can also be used to check or control the flatness of a surface.

4. Calibration of Straightedge

Straightedge calibration is about calibrating the straightness. One of the tools for straightedge calibration is a dial test gauge (test indicator). The dial gauge is set up at a certain height above a surface plate by using a dial indicator stand or height gauge, then the calibration can run. If the straightness value is not within the agreed tolerance, the straightedge needs a replacement.

This straightness error of this tool can be inspected with precision level as well. And the steps can be seen here.



Both ruler and straightedge can be used as assistance in drawing lines due to their edge is straight.


So, it is clear that the main difference between a ruler and a straightedge is their functions. The ruler makes use of its graduation to measure length or dimension. While straightedge makes use of its straight edge to measure or check the straightness of a line or surface. Aside from that, it can help you mark a straight line. In a certain situation, it can check a surface flatness as well.

However, some models can cover both of these functions. It has graduation to measure length as well as has a straight blade.