What causes Illustrator to lose Exactitude?

See below image, then read on…

Unbelievable inaccuracy

Previously this circle was 76 pixels diameter.

I changed it to 64 by manually entering it into the W: container, then tabbed, expecting 64 to appear in the H: container.

But no… I got this odd number.


How do I get it back to not doing stupid things like this?

  • It used to be accurate
  • I haven’t changed anything
  • There’s nothing turned on that wasn’t on before



“Use Preview Bounds” is probably enabled.

I can recreate what’s happened to you consistently by having this setting on.

If I turn “Use Preview Bounds” OFF ( ⌘K or ⌃K and UNCHECK “Use Preview Bounds”), then miscalculations such as this don’t occur.

Also in my testing:

  • It doesn’t matter if “Align New Objects to Pixel Grid” is turned ON
    at document creation or I enable it per object in the Transform
    palette (⇧F8), or I ignore it entirely
  • It doesn’t matter if “Snap to Grid” is ON or OFF
  • It doesn’t matter if Scale Strokes & Effects is ON or OFF
  • I can correct an object with this problem only by disabling “Use
    Preview Bounds”, then selecting the object, and then disabling
    “Constrain Width and Height Proportions” and typing new values into
    the Transform palette.
  • It happens to any path (simple, compound, or Pathfinder-created

My test went like this:
(Using Macintosh Illustrator CC 17.1.0):

  1. No documents open, Illustrator > Preferences (⌘-K) > Use Preview
    Bounds: OFF

  2. Create a new document 100px × 100px, Units: Pixels, Color Mode: RGB,Raster Effects: 72ppi, Preview Mode: Default, Align New Objects to Pixel Grid: OFF

  3. Draw a circle an arbitrary size (hit L and then Shift-Click-Drag).
    Mine came out at 59.425 px
  4. With “Constrain Width and Height Proportions” ON, adjust size of
    circle using transform palette, so it’s a true pixel dimension (I
    chose 50px)
  5. Hit ⌘-K (Illustrator > Preferences) and toggle the Use Preview
    Bounds: ON. This resized my circle to be 51 px × 51 px.
  6. Type a new Width in the Transform palette (Constrain Proportions
    still on, I chose 30) and Tab to the next field, – in my case H was
    set to 29.986px

And then I tried variants of of align to pixels etc…

Source : Link , Question Author : Confused , Answer Author : Jon

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