Fluent UI Icons and Ionicons are two of the most widely used open-source icon sets. Both are free, both ship framework packages, and both will look perfectly reasonable in a product UI — which is exactly why the choice is annoying. This page puts the two side by side using the actual artwork and the real numbers.
| Fluent UI Icons | Ionicons | |
|---|---|---|
| Icons | 20,170 | 2,607 |
| Visual variants per concept | 2 — regular and filled | 3 — outline, filled and sharp |
| Design grid | 12–48 | 24×24 |
| License | MIT | MIT |
| Attribution required | No | No |
| Official React package | @fluentui/react-icons | ionicons |
Every pair below is the same concept rendered from each library's own source files. This is the part you cannot get from a written review — the difference in stroke weight, corner rounding and optical size is the thing you will actually notice in your interface.
Enterprise applications, Microsoft 365 integrations, and products that already follow Fluent or need extremely broad coverage. The count alone means you will rarely need to look elsewhere.
Consider otherwise if: The size is also a drawback — with 20,170 icons, maintaining visual consistency across a product takes more discipline. Lucide and Heroicons are far easier to keep coherent.
Mobile and hybrid apps, cross-platform products, and interfaces that want three clear icon variants from one consistent source.
Consider otherwise if: For a more modern, minimal aesthetic, Lucide and Heroicons are the current defaults. Material Design Icons offers five themes if you need more range.
Fluent UI Icons contains 20,170 icons and Ionicons contains 2,607. Fluent UI Icons is Microsoft's icon library for the Fluent Design System, and at 20,170 icons it is the largest set indexed on IconStash. The icons are drawn across multiple sizes from 12px to 48px and in Regular and Filled styles.
Ionicons was built for the Ionic Framework and has been refined since 2013, which makes it one of the longest-maintained icon sets here. The 2,607 icons ship in three variants — Outline, Filled, and Sharp — each drawn on a 24×24 grid.
Fluent UI Icons is released under MIT. Commercial use, modification and redistribution with no attribution required.
Ionicons is released under MIT. Commercial use, modification and redistribution with no attribution required.
You do not have to commit to one. IconStash indexes both libraries, so you can search a concept once and see how each set drew it, then export SVG or PNG at any size and colour. Start with Fluent UI Icons or Ionicons, or browse every library comparison.
Both have first-party React packages: @fluentui/react-icons and ionicons. Fluent UI has the larger catalogue, so for a React app the practical difference is coverage and visual style rather than integration effort. Both tree-shake, so bundle size tracks the number of icons you import, not the size of the library.
Fluent UI Icons has 20,170 icons and Ionicons has 2,607. Fluent UI Icons is larger by about 674%. Raw count is not the whole story though — a 20,000-icon set with many near-duplicate variants can be slower to search than a tightly edited 2,000-icon set.
You can, but it usually looks wrong. Each library draws to its own grid and stroke weight — Fluent UI uses 12–48 and Ionicons uses 24×24 — so icons from both sit slightly differently next to each other. If you must mix them, keep each library to a distinct area of the interface rather than interleaving them in the same toolbar.
Fluent UI Icons is MIT: Commercial use, modification and redistribution with no attribution required. Ionicons is MIT: Commercial use, modification and redistribution with no attribution required. Neither requires payment, but attribution rules differ, so check before shipping in a product where credit is inconvenient.
Fluent UI Icons offers regular and filled; Ionicons offers outline, filled and sharp. If you need to express selected and unselected states with the same glyph, the library with more variants saves you from importing a second set.
At 16px, stroke weight and counter size matter more than coverage. Fluent UI draws on a 12–48 grid and Ionicons on 24×24. Libraries that redraw per size rather than scaling — such as Fluent UI — generally hold up best. The reliable test is to preview both at your actual render size, which you can do on any icon page on IconStash.