Phosphor Icons and Fluent UI Icons 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.
| Phosphor Icons | Fluent UI Icons | |
|---|---|---|
| Icons | 9,198 | 20,170 |
| Visual variants per concept | 6 — thin, light, regular, bold, fill and duotone | 2 — regular and filled |
| Design grid | 24×24 | 12–48 |
| License | MIT | MIT |
| Attribution required | No | No |
| Official React package | phosphor-react | @fluentui/react-icons |
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.
Design systems, products with strong visual hierarchy, and teams that want one library to cover every context. The weight range also solves the common problem of outline icons disappearing on coloured or photographic backgrounds.
Consider otherwise if: If you only need one weight, the six-weight structure is overhead you will not use — Lucide or Tabler are simpler. If you want duotone plus a premium aesthetic, compare Solar and Huge Icons.
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.
Phosphor Icons contains 9,198 icons and Fluent UI Icons contains 20,170. Phosphor is built around a single idea: one icon family that works at every weight. Each of its 9,198 icons is available in six weights — Thin, Light, Regular, Bold, Fill, and Duotone — so you can express hierarchy, hover state, and emphasis without ever leaving the library.
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.
Phosphor Icons is released under MIT. Commercial use, modification and redistribution with no attribution required.
Fluent UI Icons 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 Phosphor Icons or Fluent UI Icons, or browse every library comparison.
Both have first-party React packages: phosphor-react and @fluentui/react-icons. Phosphor has the smaller 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.
Phosphor Icons has 9,198 icons and Fluent UI Icons has 20,170. Fluent UI Icons is larger by about 119%. 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 — Phosphor uses 24×24 and Fluent UI uses 12–48 — 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.
Phosphor Icons is MIT: Commercial use, modification and redistribution with no attribution required. Fluent UI Icons 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.
Phosphor Icons offers thin, light, regular, bold, fill and duotone; Fluent UI Icons offers regular and filled. 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. Phosphor draws on a 24×24 grid and Fluent UI on 12–48. 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.