Delboeuf Circles
Delboeuf Circles — 2026, generated SVG, dimensions variable · Geometry · Still
After Joseph Delboeuf, 1865
Which inner disk is larger?
Which center circle is larger?
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Reveal the answer
The two filled center circles have the exact same radius.
↑ The mechanism, made visible.
Notes — why it looks that way
What is happening
Compare the inner filled circles, not the outer rings. On the left the gap between circle and ring is narrow; on the right it is wide. Both circles are drawn from the exact same radius value. Revealing the answer adds top and bottom guides showing that the circles’ edges line up.
Why it looks that way
Instead of measuring a circle in isolation, your visual system also uses its relationship to whatever surrounds it. A close ring and a distant ring set different comparison scales, so identical inner circles can end up feeling like different sizes. How strong this feels varies from person to person.
How to check
Hide the rings and only the two circles remain. When the rings come back, watch which direction the apparent size shifts. It is a way to separate a circle’s physical dimensions from how large it feels.
See another geometric illusion
First described
After Joseph Delboeuf, 1865
Media — images and data
- OG / X (1200×630)
- Instagram square (1080×1080)
- Shorts / Reels vertical (1080×1920)
- Answer image — landscape (X)
- Answer image — square (Instagram)
- Answer image — vertical (Shorts)
- Post drafts (JSON)
Free to use for non-commercial purposes such as classes, school projects and blogs, with a link back to this page as the credit. Commercial use is not covered
Every figure is generated here from the phenomenon itself (re-implemented). The general Delboeuf illusion principle is re-implemented here as SVG. No existing figure or code is reproduced.