## By default Autodesk Inventor will dimension the Radius of an Arc in a sketch. So how do you find the *Length *of the Arc? And what if you want to specify the Arc Length to drive your sketch?

Measuring the length of an **Arc **in an Inventor Sketch is easy. Just use the ‘**Measure Loo**p’ tool.

*Inspect Tab > Measure Panel > Loop*

*But this won’t allow you to use the Arc’s length in Parameter’s and Formula’s.*

### A Parametric Arc Length?

Unfortunately Inventor doesn’t have an ‘Arc Length’ type of Dimension Parameter in sketches. But it is pretty easy to grab the length of an Arc using a Formula.

### To Get the Length of an Arc

To get the Length of an Arc to use in your Equations you will need:

- A Model Parameter for the Included Angle of the arc –
**Angle** - A Model Parameter for the Radius of the arc –
**Radius** - A user Parameter for the Arc Length
**–****Arc Length** - A User Parameter to convert Degrees into Radians –
**Radians**

The Formula is:

`Radius * ( Radians / 1 rad )`

### To Drive the Length of an Arc

To drive the Length of an Arc you will need:

- A Model Parameter for the Included Angle of the arc –
**Angle** - A Model Parameter for the Radius of the arc –
**Radius** - A user Parameter for the Arc Length –
**Arc Length**

The Formula is:

`ArcLength * 180 deg / ( Angle * PI )`

### Visual Feedback

If you want visual feedback of the Length of the Arc you could add some sketch text, and pull in the Value you are looking for.

### Annotating an Arc’s length in an Inventor drawing

You can add a dimension annotation in an Inventor drawing to give the length of your arc using the ‘General Dimension’ tool.

*Annotate tab > Dimension Panel > Dimension Tool*

Inventor will automatically pick the radius of the Arc. Just right click to get the ‘Length’ option.

The Final result will look like this:

I hope that you enjoyed this sketching tip!

*Read this post to find out my Top Tip for creating Inventor sketches ‘Sketching – Keep it simple‘.*

Inventorexpert says

how dumb is that, it has the ability to give you the dimension in a drawing but not the ability to give you the exact same thing in a sketch. impressive inventor

Paul Munford says

I have to agree. Arc dimensioning seems like an easily solvable oversight. I would love to hear from the Inventor team why this has never been added to the package…