Radius dimension in AutoCAD: DIMRADIUS, diameter, jogged — and the override that loses the R

Drilled holes, round columns, tanks, curved wall corners: every drawing has a few places that need a radius or a diameter. A radius dimension in AutoCAD uses its own command rather than a linear one, because it must find the centre and radius of the curve by itself.

This article covers DIMRADIUS, DIMDIAMETER and DIMJOGGED in AutoCAD 2027, using the acadiso.dwt template and its default dimension style. Every result is read back from the dimension object itself: the stored measurement, the displayed text and the object type. The parts of a dimension in general are covered in dimensions in AutoCAD. For dimensioning taught properly, the Institute runs an AutoCAD course for construction.

The DIMRADIUS command and its two siblings

On the ribbon all three sit on the Annotate tab, Dimensions panel, under the Linear drop-down. The Dimension toolbar has all three as well. Locations and aliases come from the 2027 acad.cuix and acad.pgp files. According to the Autodesk documentation, the DIMRADIUS command creates a radius dimension for a circle or an arc.

Placing a radius dimension, step by step

Type DRA and the 2027 release asks two questions:

Between them the command line announces the value, for example Dimension text = 400. A circle of radius 400 is labelled R400. The R is added for you.

Three kinds of object, one method:

At step 1 you must click on the curve itself. Click the centre or empty space inside and the prompt Select arc or circle: simply repeats. Click an existing dimension lying over the curve and AutoCAD says Object selected is not a circle or arc.

Diameter dimension in AutoCAD with DIMDIAMETER

Type DDI; the two prompts are the same as for DIMRADIUS. On the same circle of radius 400 it reports Dimension text = 800 and labels it Ø800: the diameter, twice the radius.

The diameter symbol it adds is stored in the dimension text as the code \U+2205, the Unicode character "⌀". To type that symbol yourself in ordinary text such as notes or rebar schedules, see the diameter symbol in AutoCAD.

A diameter dimension in AutoCAD is not limited to full circles. Select the arc of radius 300 and DIMDIAMETER labels it Ø600, the diameter of the circle the arc belongs to. Both commands accept the same objects; only the number and the prefix differ.

Which one to use? Holes, pipes and round columns usually take a diameter, the figure used to buy material or choose a drill bit. Fillets, curved walls and road curves usually take a radius, the figure used to set out the shape on site.

DIMJOGGED: a large radius whose centre is off the sheet

A road curve of several hundred metres or a stadium's curved wall has its centre far outside the drawing frame, so the dimension line cannot run back to it. DIMJOGGED uses a "centre override": a jogged dimension line starting from a point you pick near the arc.

On an arc of radius 300 with the centre override placed elsewhere, the text is still R300: the value is the true radius, not the distance to the substitute centre. The object created is a separate type, LARGE_RADIAL_DIMENSION, unlike the DIMENSION type of the other two.

Text along the dimension line, or at a fixed angle

With the default acadiso.dwt dimension style the text runs along the dimension line. Place it at different spots around the same circle and its angle changes:

The Angle option at the second prompt fixes the text angle whatever the direction of the dimension line. On a plan full of round holes, choose A and type 0 each time so every value reads horizontally. The text may also sit inside the circle; just click inside it. For small holes, click outside instead.

Summary of the three commands

The last column is the number AutoCAD stores, which matters for quantity take-off or for a LISP routine that reads dimensions. It is always the true measurement, even when the displayed text has been typed over, as below.

Typing over the value: the trap that loses the R

At the text placement prompt, T (Text) lets you type text in place of the value. This is where many drawings go wrong unnoticed:

Typing a number replaces the R along with the value, so readers cannot tell a radius from a diameter. The <> pair stands for the true measurement: type <> plus your extra words and AutoCAD keeps R400 and appends your text.

There is a second reason not to type over values: a dimension that keeps its true value follows the geometry. Change the circle's radius from 400 to 500 and the dimension becomes R500. The one typed over as 400 still shows 400, while its stored measurement is now 500. The drawing says one thing, the geometry another, and nothing warns you.

A worked order for a plan with holes and curves

Putting the results together, here is a safe order for a slab plan with four round openings and one curved edge:

1. Draw the openings as circles and the edge as an arc or a polyline arc segment; there is no need to explode the polyline.
2. Dimension each opening with DDI, clicking on the circle itself, never on its centre. Use A and 0 if all values should read horizontally.
3. Dimension the curved edge with DRA. If its centre falls outside the sheet, use DJO and place the centre override inside the frame.
4. When you need a note such as "4 holes", type <> followed by the note at the Text option, so the Ø or R and the true value stay.
5. Never type a bare number over a value. If the openings are later resized, every dimension that kept <> updates by itself.

With that order the plan stays correct through revisions. The only dimensions that can drift away from the geometry are the ones typed over, and step 5 removes them.

Three things often repeated that are not true

Frequently asked questions

Which command gives a radius dimension in AutoCAD?

DIMRADIUS, alias DRA. Select a circle or arc, then click where the text goes.

How do I dimension a diameter?

Use DIMDIAMETER, alias DDI. The value gets the Ø prefix automatically.

Why won't it accept my circle?

You clicked the centre or empty space inside. Click on the curve itself.

Why is there no R in front of the value?

The value has been typed over. Change the text back to <> and the R and the true value return.

How do I dimension a radius whose centre is off the drawing?

Use DIMJOGGED (alias DJO): select the arc, pick a substitute centre nearby, place the text, then the jog.

Is the true value lost when the text is typed over?

No. A dimension typed over as 400 still stores its real measurement; only the displayed text changes. Set the text back to <> to show it again.