AutoCAD · Dimensioning
No matter how beautifully you draw something, a drawing without dimensions is just a picture. At the end of the day, machinists and vendors only care about the numbers — and trust me, missing a single dimension is all it takes to get a phone call you didn’t want. On the flip side, a drawing with clean, well-organized dimensions speaks for itself and builds instant credibility.
“From setting up DIMSTYLE to mastering Baseline and Continue dimensions — here’s everything you need to know about AutoCAD dimensioning, all in one place.”
In this post, we’ll walk through how to configure the Dimension Style Manager (DIMSTYLE), the essential dimensioning commands for linear, aligned, baseline, and continue dimensions, and the all-important DIMSCALE formula — step by step.
1. Dimension Style Manager (DIMSTYLE · Shortcut: D)
Before you start placing dimensions, you need to set up a Dimension Style first. Think of it as a template that controls everything — text height, arrowhead shape, spacing between dimension lines and extension lines, and more.
- How to open it: Type D or DIMSTYLE → Enter → The Dimension Style Manager dialog will pop up.
- By default, AutoCAD comes with an ISO-25 style already set up. In practice, though, most people either modify it (Modify) or create a brand-new style (New) to match their company’s drawing standards.
Inside the Style Manager, you’ll find several tabs. Let’s go through the ones that really matter in real-world drafting.
2. Lines Tab — Dimension & Extension Lines
This is where you control the geometry of the lines that make up your dimensions.
- Baseline spacing: When using Baseline Dimension (DIMBASELINE), this setting determines how far apart each stacked dimension line sits — so they don’t overlap. A value of 7–10 mm works well in most cases.
- Extend beyond dim lines: This is how far the extension lines stick up past the dimension line — that little overshoot at the top. Typically set to 1–2 mm.
- Offset from origin: Controls the gap between the object being dimensioned and where the extension line starts. Setting it to around 1–2 mm keeps extension lines from touching the geometry, which makes the drawing look a lot cleaner.
3. Symbols and Arrows Tab — Arrowhead Settings
Here you can change the style and size of the arrowheads at the ends of your dimension lines.
- For mechanical drawings, Closed Filled arrowheads are the standard. In architectural drafting, you’ll often see Oblique (tick marks) or Dot styles instead.
- Arrow size: A size of 2.5–3 mm is typical. You can adjust this based on your drawing scale.
4. Text Tab — Dimension Text Settings
This tab controls how the dimension numbers look and where they sit relative to the dimension lines.
- Text height: Set this to a size that’s easy to read when printed. 2.5–3.5 mm is a common range for mechanical drawings.
- Offset from dim line: The gap between the dimension number and the dimension line itself. Around 0.625–1 mm tends to look right.
- Vertical position: Set to Centered and the dimension line splits around the text — common in mechanical drafting. Set to Above and the text sits on top of an unbroken line — standard in architectural drawings.
- Text alignment: If you choose “Aligned with dimension line,” the text will rotate to match the angle of the dimension — great for angled dimensions on diagonal geometry.
5. Fit Tab — Overall Scale (DIMSCALE)
This is the tab that trips up beginners the most. If your dimension text looks way too tiny — or laughably huge — after placing it, this is almost certainly where the problem is.
- Use overall scale of (DIMSCALE): This is the DIMSCALE variable. All the values you set in tabs 2–4 (text height, arrow size, offsets, etc.) are calibrated for a 1:1 drawing. DIMSCALE is a multiplier that scales all of those values up or down at once.
- The default is 1. For a 1:1 drawing, leave it as is.
- If you’re working on a 1:2 scale drawing, keep the geometry untouched and change DIMSCALE to 2. Your dimension text, arrows, and offsets will all double in size to match the scale.
- For a 1:4 scale drawing? Same deal — leave the geometry alone and set DIMSCALE to 4.
5-1. Understanding Scale with an A3 Sheet Example
Let’s make this concrete with an A3 sheet example. When drafting in AutoCAD, you never change the size of the geometry itself. The actual shapes are always drawn at true 1:1 size. What you scale up is the sheet border and the dimension elements (text, arrows, offsets) — not the drawing.
| Drawing Scale | Sheet (A3 basis) | Dimension Elements (DIMSCALE) | Geometry (Model) |
|---|---|---|---|
| 1:1 | A3 standard size × 1 | DIMSCALE = 1 | True size — unchanged |
| 1:2 | A3 standard size × 2 | DIMSCALE = 2 | True size — unchanged |
| 1:4 | A3 standard size × 4 | DIMSCALE = 4 | True size — unchanged |
The geometry in your CAD drawing is the source of truth for machining and manufacturing — CNC machines and other equipment read those coordinates directly. If you scale the model down to match a 1:2 print, the machine will produce a part that’s half the intended size. That’s why the rule is absolute: keep the model at true 1:1, and only adjust the sheet border and dimension scale factor.
DIMSCALE = the denominator of the scale ratio. 1:1 → DIMSCALE = 1. 1:2 → DIMSCALE = 2. 1:100 → DIMSCALE = 100. Change this one value and everything — text, arrows, offsets — scales proportionally. In practice, many drafters copy a base style and just update the DIMSCALE for each different scale they work with.
6. Primary Units Tab — Number Format & Precision
This tab controls how the actual dimension values are displayed.
- Unit format: Decimal is the go-to for virtually all mechanical drafting.
- Precision: Sets how many decimal places to show. Most mechanical drawings use one decimal place (0.0) or even whole numbers (0). For tight-tolerance work, 2–3 decimal places may be needed.
- Trailing zeros — Suppress: Enable this and “100.00” displays as “100” instead. A small thing, but it keeps drawings looking tidy and professional.
7. Linear Dimension (DIMLINEAR · Shortcut: DLI)
This is the bread-and-butter dimension command. It measures the horizontal or vertical distance between two points.
- Basic usage: DLI → Enter → Click first point → Click second point → Click to place the dimension line
- Rotated dimension (R option): DLI → Enter → Click two points → Type R (Rotated) → Enter → The dimension line will tilt to match the angle. This is actually a slicker approach than using DIMALIGNED in many cases — one less command to remember.
8. Aligned Dimension (DIMALIGNED · Shortcut: DAL)
This command measures the true distance between two points and places the dimension line parallel to the line connecting them. Perfect for diagonal or angled geometry.
- Basic usage: DAL → Enter → Click first point → Click second point → Click to place the dimension line
- Since the Rotated option in DIMLINEAR can handle angled dimensions too, DAL sees less use in day-to-day drafting. That said, when you just need a quick true-length dimension without any extra input, DAL is the more straightforward choice.
9. Baseline Dimension (DIMBASELINE · Shortcut: DBA)
This command measures the cumulative distance from a single shared origin point to multiple locations. Each new dimension line steps up from the previous one in a stacked arrangement.
- Prerequisite: You need to place a linear dimension (DLI) first. The first extension line of that dimension becomes the baseline origin.
- Basic usage: DBA → Enter → Select the base dimension (it defaults to the last one placed) → Click the next point → Repeat → ESC to exit
- Since DBA shows total accumulated distance from the origin, it’s especially useful in CNC machining where everything is measured from a fixed datum point.
10. Continue Dimension (DIMCONTINUE · Shortcut: DCO)
This command picks up right where the last dimension left off, chaining dimensions end-to-end in a single row.
- Prerequisite: Like DBA, you need a linear dimension (DLI) already placed.
- Basic usage: DCO → Enter → Click the next point → Repeat → ESC to exit
- DCO shows individual segment lengths rather than cumulative distances — ideal when you need to call out each step of a part independently.
Baseline (DBA) gives you cumulative distances from a single origin — think CNC coordinates where everything references zero. Continue (DCO) gives you individual segment lengths in sequence — think stepped shafts where each section has its own length. In practice, both often appear on the same drawing — DBA for overall positioning, DCO for segment-by-segment detail.
11. Other Commonly Used Dimension Commands
- Angular Dimension (DAN): Measures the angle between two lines. Click each line in sequence, then click to place the dimension arc.
- Radius Dimension (DRA): Dimensions the radius of a circle or arc. Click the arc and AutoCAD automatically prefixes the value with “R”.
- Diameter Dimension (DDI): Dimensions the diameter of a circle. The “Ø” symbol is added automatically.
- Quick Dimension (QDIM): Select multiple objects at once and batch-generate baseline or continue dimensions in one shot. A real time-saver when you have a lot of repetitive dimensioning to do.
Dimension Commands at a Glance
| Command | Shortcut | What It Does |
|---|---|---|
| DIMSTYLE | D | Dimension Style Manager — the starting point for all dimension settings |
| DIMLINEAR | DLI | Horizontal / vertical linear dimension |
| DIMALIGNED | DAL | True-length dimension along angled geometry |
| DIMBASELINE | DBA | Cumulative distances from a shared origin |
| DIMCONTINUE | DCO | Chained dimensions continuing from the last endpoint |
| DIMANGULAR | DAN | Angle between two lines |
| DIMRADIUS | DRA | Radius (R) of a circle or arc |
| DIMDIAMETER | DDI | Diameter (Ø) of a circle |
| QDIM | QDIM | Batch-generate dimensions across multiple objects |
Speaking from experience, the vast majority of real-world mechanical drawings can be handled with just four commands: Linear (DLI), Diameter (DDI), Radius (DRA), and Angular (DAN). Get those four down cold and you’re covered for almost anything. Continue (DCO) comes in handy occasionally, too.
Custom Shortcuts for Dimension Commands — Using LISP
DLI, DAL, DBA, DCO… once you’re used to them, they’re fast enough. But let’s be honest — when you’re first starting out, those multi-letter shortcuts are easy to mix up. With a LISP file, you can remap any command to whatever shortcut feels most natural to you.
For example, with the setup below, you can type D1 instead of DLI to fire off a linear dimension instantly.
| LISP Shortcut | Original Command | Function |
|---|---|---|
| D1 | DIMLINEAR | Linear dimension |
| D2 | DIMALIGNED | Aligned dimension |
| D3 | DIMANGULAR | Angular dimension |
| D4 | DIMRADIUS | Radius dimension |
| D5 | DIMDIAMETER | Diameter dimension |
You can also remap shortcuts by editing AutoCAD’s acad.pgp file — but here’s the problem: every time you reinstall AutoCAD or work on a different machine, those settings get wiped. A LISP file, on the other hand, is completely portable. Stick it on a USB drive and you have your personalized shortcut setup wherever you go. If you work across multiple machines or share setups with colleagues, LISP is the way to go. Check out the link below for a detailed guide on how to set it up.
Wrapping Up
When it comes to dimensioning in AutoCAD, the single most important thing you can do is set up your Dimension Style (DIMSTYLE) properly from the start. Once that’s dialed in, the workflow basically runs itself: place a baseline with DLI, then chain the rest with DBA or DCO.
- DIMSCALE = the denominator of your scale ratio — remember this one formula and you’ll never wonder why your dimensions look too small or too big again.
- Four commands cover most drawings: DLI, DDI, DRA, DAN. Learn those first.
- For repetitive work, DBA, DCO, and QDIM will save you serious time.