Object snap in AutoCAD decides whether a drawing is actually accurate. The human eye cannot place a crosshair exactly on the end of a line, so without snapping every line lands a few units out — the drawing looks right and measures wrong.
This article is written so you can follow along at the machine: how to switch snapping on, which modes a building drawing needs, how to call one mode for a single pick, and above all how to fix it when the program refuses to snap. To learn modelling and documentation end to end, see the AutoCAD for construction course.
Where to start object snap
Read straight out of the 2027 configuration files, and the answer is a little surprising.
| Route | Detail |
|---|---|
| Full command | OSNAP, opens the settings dialog |
| Alias | OS, and also DDOSNAP |
| Keyboard | F3 toggles it, F11 toggles object snap tracking |
| Ribbon | no button |
| Classic menu | no entry |
| Toolbar | Object Snap → Osnap Settings |
| Command line version | -OSNAP, set by typing names |
There is no ribbon button and no menu entry, because what people actually click is the Object Snap button on the status bar at the bottom of the screen, which is not a command at all. F3 does the same job faster.
The prompts, step by step
The -OSNAP form asks a single question, copied verbatim.
| Step | What the program asks | What you do |
|---|---|---|
| 1 | Enter list of object snap modes: | Type the modes you want, separated by commas |
Typing end,mid,cen,int turns on exactly those four and turns every other mode off. It is the only way to set the whole running snap in one line, which makes it ideal inside a script or a drawing-setup routine.
Typing none turns everything off. And to use one mode just once, type its name while a command is asking for a point; nothing needs to be switched on first.
Turning object snap on: F3 and the settings dialog
The quickest way is to press F3. Press it again to switch snapping off. The status bar at the bottom of the screen carries the matching button.
To choose which modes are active, open the settings dialog:
- Type
OSand press Enter, or typeDSETTINGSand press Enter. - The Drafting Settings dialog opens on the Object Snap tab.
- Tick the modes you need and click OK.
| No. | Item | What it does |
|---|---|---|
| 1 | Object Snap On | Master switch for the whole group. The label names the shortcut, F3 |
| 2 | Object Snap Tracking On | Switches tracking from acquired points. Shortcut F11 |
| 3 | Left-hand column | Endpoint, Midpoint, Center, Geometric Center, Node, Quadrant, Intersection |
| 4 | Right-hand column | Extension, Insertion, Perpendicular, Tangent, Nearest, Apparent intersection, Parallel |
Four function keys belong together, so learn all four:
| Key | Mode | What it does |
|---|---|---|
| F3 | Osnap | Object snap — endpoints, midpoints, intersections |
| F8 | Ortho | Locks the cursor to horizontal and vertical |
| F10 | Polar | Tracks the angles you declared, every 45 degrees for instance |
| F11 | Otrack | Tracks along lines through points you have acquired |
A new drawing turns on four modes, and misses the one you need
Here is something few people notice. AutoCAD has fourteen object snap modes, but a new drawing switches on only four: Endpoint, Center, Intersection and Extension.
Check it on your own machine: type OSMODE and press Enter. On a fresh 2027 install the value comes back as 4133. That is the sum of four numbers: 1 for Endpoint, 4 for Center, 32 for Intersection and 4096 for Extension.
The trouble is that those four are not enough for building work. The critical gap is Midpoint, because wall centrelines and door centrelines all need the middle of a line. Switch on Midpoint and Perpendicular from the start.
Equally, do not switch on all fourteen. With too many active the cursor jumps about, because too many candidate points sit close together. Around six everyday modes is right; call the special ones as you need them. Tuning object snap in AutoCAD is mostly this one judgement: enough modes to work quickly, few enough that the cursor stays predictable.
Nearest deserves its own warning: leave it on and every pick lands on the nearest line, masking every other mode.
Read the marker to see where the snap will land
Each mode draws its own marker at the point it is about to snap to, with the mode name beside it. Recognise the marker and you know where the pick will land without reading the command line.
One thing confuses nearly every beginner, and Autodesk states it plainly: object snaps only work while a command is asking for a point. The wording is "Object snaps work only when you are prompted for a point", on the About Using Object Snaps page.
So moving the cursor around with no command running shows no marker at all, and that is correct behaviour. Many people assume snapping is off and keep toggling it.
Calling one mode for a single pick
When you need a mode you do not want running permanently, call it once. A one-time override applies only to the next point you pick; it never changes the running settings.
Method one — the menu. Hold Shift and right-click.
The first group holds four special tools, and the first two are the ones worth learning for building work:
| Item | What it does |
|---|---|
| From | Takes a base point then an offset. This is the tool for placing a door in a wall: snap to the wall corner, then type the offset to the door reveal |
| Mid Between 2 Points | The midpoint of any two points, even with no line joining them. Use it to find the centre of a room |
| Temporary track point | A temporary reference point for tracking, when you need to line up from two directions |
| None | Suppresses snapping for exactly one pick, when you want a free point right beside an existing line |
Method two — type the first three letters. Faster than the menu, and it leaves a trace on the command line: MID, CEN, END, INT, PER, TAN, NEA.
Try it now: draw a rectangle with a circle inside it, then join the middle of the bottom edge to the centre of the circle.
- Type
Land press Enter. At the first point prompt, typeMIDand press Enter. The program repliesofand waits for you to pick a line. Pick near the middle of the bottom edge. - At the next point prompt, type
CENand press Enter, then click anywhere on the circle. The point captured is the centre, not where you clicked. Press Enter to finish. - Check it with
LIST: the line runs from the exact midpoint of the bottom edge to the exact centre. Clicking a few hundred units off makes no difference, because the snap pulls the point to the right place.
With PER and TAN the prompt changes from of to to. PER drops the foot of a perpendicular, so a line drawn from any point to a vertical line using PER always comes out horizontal.
To list the modes currently running, type -OSNAP, the command-line form of the dialog. On a fresh install it prints Current osnap modes: End,Cen,Int,Ext — matching the value 4133.
Snaps that fail: the real cause is OSOPTIONS
This is what people search for most, and where the worst advice circulates. Plenty of sites suggest saving to DXF and reopening, or resetting the UCS to World. Those rarely address the actual cause.
The real cause is usually the OSOPTIONS system variable. Autodesk documents its default as 7, and 7 is the sum of the three values below — meaning AutoCAD suppresses snapping by default in all three places:
| Value | AutoCAD ignores snaps on |
|---|---|
| 1 | hatch objects |
| 2 | geometry with a negative Z while a dynamic UCS is in use |
| 4 | the endpoints of dimension extension lines |
That answers the common question about hatches: nothing is broken, it is the default setting. Type OSOPTIONS and press Enter, then set a new value — subtract 1 to snap to hatches, subtract 4 to snap to extension-line ends, or set 0 to allow all three. The detail sits on the OSOPTIONS (System Variable) page.
If OSOPTIONS is already right and snapping still fails, work down this list:
- Is F3 on? The status bar button is lit when it is.
- Is the mode you want ticked? Snapping to a midpoint never works while Midpoint is unticked.
- Is a command actually asking for a point? No command means no marker, exactly as Autodesk describes.
- Is the target box too small? Its size comes from the
APERTUREvariable, measured in pixels and set on the Drafting tab of theOPTIONSdialog. A small box forces you to hover very close. - Are too many modes on? The cursor hops between candidate points, which looks like snapping to the wrong thing.
Tracking and polar: a point at the crossing of two directions
These two work alongside snapping and do something snapping alone cannot.
Polar tracking switches on with F10. It draws a faint guide whenever the cursor approaches one of the declared angles. By default only multiples of 90 degrees are declared — horizontal and vertical.
Object snap tracking switches on with F11. To use it, move the cursor over a snap point and pause there without clicking. A small cross appears to confirm the point is acquired, and a guide runs from it.
Combining the two places a point at the crossing of two directions without drawing a single guide line: acquire the midpoint of the top edge, acquire the midpoint of the left edge, then move into the middle. Where the two guides cross is the centre of the shape.
Frequently asked questions
What is the object snap command in AutoCAD?
Type OS and press Enter for the dialog, or press F3 to toggle it. The command-line form is -OSNAP, useful for declaring a list of modes without opening the dialog.
How do I turn object snap off?
Press F3. To suppress it for a single pick only, hold Shift, right-click and choose None.
Why can I not snap to a hatch?
Because OSOPTIONS defaults to 7, and the value 1 within it tells AutoCAD to ignore hatch objects. Type OSOPTIONS and set a value with 1 subtracted.
My snapping jumps around — how do I stop it?
Usually too many modes are running at once, Nearest especially. Cut back to about six everyday modes and call the rest one pick at a time.
How do I see which modes are currently on?
Type OSMODE and press Enter to read the number, or type -OSNAP to have the program print the mode names.
Related articles
- What is AutoCAD — a handbook for people working in construction
- How to draw an arrow in CAD — MLEADER annotation, solid arrows and symbol arrows
- What advanced AutoCAD covers — ten job skills once the drawing commands are second nature
- How to read construction drawings — conventions on plans and sections