Most lines on a floor plan are horizontal or vertical: walls, grid lines, beams. Dragging by hand is never perfectly straight; a slight wobble makes a slanted line that will not join properly. F8 in AutoCAD solves this: press F8 to turn on Ortho mode and every line drawn with the mouse is forced horizontal or vertical.
But Ortho has places where it does not force anything, and that is the source of many "why is my line still slanted" questions. This article tests each case with real mouse clicks. To learn precise drawing aids properly, the Institute runs an AutoCAD course for construction.
F8 is a key, not a command
F8 is a function key, not a command name. Pressed at the Command: prompt, it switches the ORTHOMODE variable from 0 to 1, and back to 0 on the next press. Four ways do the same thing:
| Route | What to do |
|---|---|
| F8 key | Toggle Ortho |
| Ctrl+L | Toggle Ortho; the acad.cuix file assigns this key to Toggle Ortho |
Type ORTHO | AutoCAD asks Enter mode [ON/OFF] <OFF>:; type ON or OFF |
| Ortho Mode button on the status bar | Click to toggle |
The value in angle brackets of the ORTHO prompt is the current state: <OFF> when off, <ON> when on. It tells you where Ortho stands without hunting for the status bar button.
How Ortho mode in AutoCAD forces a mouse click
On the 2027 release: type LINE, first point 0,0, then click a point towards the upper right, at exactly the same screen spot both times.
| Ortho | End point of the line |
|---|---|
| Off | (1238.9, 573.8), exactly where clicked, slanted |
| On | (1238.9, 0.0), horizontal |
Ortho keeps the larger component of the movement and drops the smaller. Here the horizontal move of 1238.9 beats the vertical 573.8, so the line goes horizontal. Clicking higher up near the vertical axis, where the vertical move is larger:
| Click position | End point with Ortho on |
|---|---|
| Far right, slightly up | (1238.9, 0.0), horizontal |
| Near the vertical axis, high up | (0.0, 811.4), vertical |
There is no need to choose horizontal or vertical beforehand; Ortho decides from the direction you move. In practice this means you can sketch the outline of a room by moving the mouse roughly along each wall and clicking, and every segment comes out exactly horizontal or vertical without a single typed coordinate; close the last corner with an Endpoint snap.
The Autodesk documentation describes Ortho as a way to "restrict the cursor to the horizontal or vertical directions relative to the user coordinate system (UCS)". "Relative to the UCS" matters: rotate the UCS and Ortho's horizontal and vertical rotate with it. See our article on the UCS.
Where Ortho does not apply: typed coordinates
Still with Ortho on, type LINE, first point 0,0, next point @500<30, i.e. 500 long at 30°. The line comes out slanted at exactly 30°, ending at (433, 250). Ortho leaves typed coordinates alone. The same holds for absolute coordinates: typing 433,250 as the second point gives the identical slanted line, because the point is fully defined before Ortho gets a say. Ortho only ever decides where a free mouse click lands.
Autodesk states the rule: "Ortho is ignored when you enter coordinates or specify an object snap." So:
| You do | Does Ortho apply |
|---|---|
| Click in empty space | Yes |
| Type absolute or relative coordinates | No |
| Snap to an endpoint or midpoint of an existing line | No |
If Ortho is on and a line still slants, its end point almost certainly came from typed coordinates or an object snap: Ortho is not broken, it is following its rule. Typing coordinates is covered in entering coordinates, object snaps in object snaps.
Ortho with typed distances
Ortho shines with "direction by mouse, length by keyboard". Autodesk's tip: "Use direct distance entry with Ortho mode turned on to create horizontal and vertical lines of specified lengths, or to move or copy objects horizontally or vertically for specified distances." Turn Ortho on, start LINE, pick the first point, move the mouse towards where you want to go, then type a number such as 3600 and Enter.
| Ortho | Move the mouse up and to the right, type 3600 | End point |
|---|---|---|
| On | A horizontal line 3600 long | (3600, 0) |
| Off | A line 3600 long, slanted along the mouse direction | (3266.7, 1512.9) |
Same action, only F8 differs. With Ortho on, the 3600 lands exactly on the horizontal axis.
Ortho and polar tracking cannot run together
Polar tracking guides lines along preset angles such as 30° or 45°. With Polar on (the Polar bit of AUTOSNAP set, value 63), pressing F8 on the 2027 release gives:
| Press | ORTHOMODE | Polar |
|---|---|---|
| Before | 0 | On (AUTOSNAP = 63) |
| F8 once | 1 | Turned off (AUTOSNAP = 55) |
| F8 twice | 0 | Still off |
| Then F10 | 0 | On again |
Autodesk confirms: "Ortho mode and polar tracking cannot be turned on at the same time. Turning on Ortho turns off polar tracking." Turning Ortho off does not bring Polar back; F10 does. Drawing at angles is covered in drawing angles.
AutoCAD function keys next to F8
Many people hit F7 or F9 when reaching for F8, then find a grid appearing or the cursor jumping in steps. Pressing each key on the 2027 release and reading the system variables before and after:
| Key | Variable changed | Toggles |
|---|---|---|
| F3 | OSMODE gains bit 16384 | Object snap |
| F4 | 3DOSMODE | 3D object snap |
| F5 | SNAPISOPAIR 0 → 1 → 2 | Isometric plane, cycling three planes |
| F6 | UCSDETECT | Dynamic UCS |
| F7 | GRIDMODE | Grid |
| F8 | ORTHOMODE | Ortho |
| F9 | SNAPMODE | Snap, cursor jumps in steps |
| F10 | AUTOSNAP bit 8 | Polar tracking |
| F11 | AUTOSNAP bit 16 | Object snap tracking |
| F12 | DYNMODE | Dynamic input by the cursor |
Pressing the same key twice restores it, except F5, which cycles through three planes.
If the cursor suddenly jumps in fixed steps and will not land where you click, check F9: Snap is on. A dotted grid appearing out of nowhere is F7. Object snap markers vanishing while you draw is F3, which leaves your chosen snap modes in OSMODE but switches them all off at once, so pressing F3 again brings the same set back. Knowing which key did what saves the usual scramble through the Drafting Settings dialog.
Ortho in 3D views
Ortho does not stop at the drawing plane. Autodesk explains: "In 3D views, Ortho mode additionally restricts the cursor to the up and down directions. In that case, the tooltip displays a +Z or -Z for the angle." In an isometric 3D view, then, Ortho offers a third direction, straight up or down, alongside the two horizontal ones. That makes it just as useful for drawing columns and vertical pipe runs in a 3D model as for walls on a plan.
When to turn off Ortho
Ortho helps on plans and elevations, where nearly every line runs along a grid axis, and on sections through walls and slabs. It gets in the way when clicking slanted points such as a roof apex, a stair stringer or a chamfer, because every free click is pulled back to horizontal or vertical. Press F8 to turn off Ortho, draw the slanted line, press F8 again. If the slanted point can be snapped to, there is no need to turn it off at all, because Ortho ignores object snaps.
Three things often repeated that are not true
| Often repeated | What holds on the 2027 release |
|---|---|
| With Ortho on you cannot draw a slanted line | Typed coordinates and object snaps still give slanted lines |
| Turning Ortho off turns Polar back on | Polar stays off; turn it on yourself with F10 |
| F8 is the name of a command | F8 is a key; the command is ORTHO and the variable is ORTHOMODE |
Understanding these three points explains nearly every surprise people have with F8 in AutoCAD.
Frequently asked questions
What does F8 do in AutoCAD?
It toggles Ortho mode, forcing lines drawn with the mouse horizontal or vertical. It switches the ORTHOMODE variable between 0 and 1, and when it turns Ortho on it also turns Polar tracking off if Polar was on.
Ortho is on, so why is my line still slanted?
The end point was typed as coordinates or snapped to an object. Ortho ignores both.
Which other keys toggle Ortho?
Ctrl+L, the ORTHO command, or the Ortho Mode button on the status bar.
Why did Polar disappear after I pressed F8?
Turning Ortho on turns Polar off, and turning Ortho off does not bring it back. Press F10 to turn Polar on.
How can I tell whether Ortho is on?
Type ORTHO: the value in angle brackets is the current state. Or read ORTHOMODE; 1 means on.
Does Ortho follow a rotated UCS?
Yes. Ortho works along the horizontal and vertical of the current UCS.