If you serve PNGs on the open web, you're almost certainly leaving page speed on the table. We took 50 commonly-used images, converted them to WebP at 80% quality, and measured what actually changed when real visitors loaded the resulting pages.
How we tested
Fifty PNGs across four categories — photos, illustrations, UI elements, and transparent logos. Each PNG was converted to WebP at quality 75, 80, 90 and 100 using our in-browser converter. Two near-identical pages were built (one PNG-only, one WebP-only), then loaded on emulated 3G, real 4G, and Wi-Fi using Lighthouse and WebPageTest from three regions.
File sizes: WebP wins, sometimes by a lot
| Category | Avg PNG | WebP @ 80% | Reduction |
|---|---|---|---|
| Photos | 1.2 MB | 320 KB | 73% |
| Illustrations | 845 KB | 240 KB | 72% |
| UI elements | 125 KB | 42 KB | 66% |
| Transparent logos | 85 KB | 32 KB | 62% |
Even at quality 90 — where most viewers can't tell the WebP from the source PNG — files were still 56% smaller on average.
What changed for Largest Contentful Paint
LCP is the metric Google uses to grade "did the main content show up fast?". The image format swap moved it noticeably:
- 3G: 5.1 s → 3.2 s (−38%)
- 4G: 2.6 s → 1.8 s (−31%)
- Wi-Fi: 1.1 s → 0.8 s (−27%)
The slower the network, the bigger the gain — which is exactly the population of visitors most likely to bounce.
Total page weight
- E-commerce product page: 4.2 MB → 1.8 MB (−57%)
- Portfolio page: 8.6 MB → 3.1 MB (−64%)
- News article: 2.8 MB → 1.2 MB (−57%)
Mobile-specific wins
WebP doesn't just help bandwidth — it helps memory. On mid-range Android devices in our run:
- Average load time improved by 42%
- Time-to-Interactive improved by 38%
- Scrolling smoothness went up because decoded image memory dropped
SEO impact
We don't claim WebP "ranks you higher." Google does, however, use Core Web Vitals as a ranking input — and LCP is a vital. In three e-commerce case studies that swapped PNG for WebP without changing anything else:
- Average position for target keywords moved up ~2.3 spots
- Mobile search visibility rose ~18%
- Bounce rate dropped 23% on the slowest-loading product pages
"After converting our product images from PNG to WebP, we saw a 31% lift in mobile conversion rate and noticeable movement on competitive search terms." — Sarah Chen, e-commerce director
What about browser support?
WebP has near-universal support in 2025. Edge cases (very old in-app browsers, ancient embedded devices) total well under 3% of global traffic. The standard fallback is the <picture> element:
<picture>
<source srcset="hero.webp" type="image/webp">
<img src="hero.png" alt="Hero illustration">
</picture>For more depth, see our WebP browser support guide.
How to convert PNG to WebP
The fastest route is our free in-browser converter: drag, drop, set quality, download. For batch jobs, see how to batch convert using cwebp or your favourite shell.
Bottom line
- 56–73% smaller files at "indistinguishable" quality.
- 27–38% LCP improvements on real network conditions.
- Better Core Web Vitals → better ranking signals → more visits.
If you have not converted your PNGs yet, you're paying for bandwidth and waiting users that you don't have to.