Pixel count, megapixels, and what they tell you
Pixel count is the raw number of pixels in an image (width × height). Megapixels (MP) is the same number divided by a million, used because the raw numbers get unwieldy. A 1080p frame is about 2 MP; UHD 4K is about 8.3 MP; 8K is about 33 MP; a typical mirrorless camera shoots 24–60 MP.
Pixel count drives everything downstream: file size scales linearly with it, processing time scales linearly with it, GPU memory needed for editing scales linearly with it, and the network bandwidth to ship the file scales linearly with it. Doubling each dimension quadruples pixel count, which often quadruples the file size — that's why "let's just shoot in 4K, we'll downscale later" can blow up project storage faster than expected.
Scale ratios — when you need to upscale or downscale
Going from 1080p (1920×1080) to UHD 4K (3840×2160) is an exact 2× upscale in each dimension. Going from 1080p to 2K QHD (2560×1440) is 1.33× — a less clean ratio. The calculator shows the scale factor between any two resolutions, which matters for two reasons:
- Quality. Integer ratios (2×, 3×) produce the cleanest upscales because every source pixel maps to a whole-number block of output pixels. Non-integer ratios require interpolation, which softens detail slightly.
- Performance. Resizing to an integer multiple is often hardware- accelerated; resizing to an arbitrary size goes through a slower interpolation path.
File size estimates — calibrated to real-world averages
The size estimates assume typical photographic content encoded at standard quality settings:
- PNG: 1.5 bytes/pixel — lossless compression at typical photo content's compressibility.
- JPG q90: 0.5 bytes/pixel — lossy at "looks identical to the source" quality.
- WebP q80: 0.35 bytes/pixel — ~30% smaller than JPG at matching visual quality.
- AVIF q70: 0.25 bytes/pixel — most efficient mainstream codec.
- Uncompressed: 4 bytes/pixel — raw RGBA. Mostly useful for memory estimates during editing, not files on disk.
Real-world numbers vary by content. Flat-color images (charts, screenshots) compress 3–5× better than these estimates; high-detail scenes (foliage, crowds) can be worse. Treat the estimates as order-of-magnitude.
Resolution names you'll see and their actual pixel counts
Marketing names hide a lot. A short cheat sheet:
- HD / 720p — 1280×720 (0.9 MP)
- Full HD / 1080p / 2K (loose) — 1920×1080 (2.07 MP)
- 2K / QHD / 1440p — 2560×1440 (3.69 MP)
- UHD 4K — 3840×2160 (8.29 MP). The "4K" most people mean.
- DCI 4K — 4096×2160 (8.85 MP). Theatrical cinema standard.
- 5K (iMac) — 5120×2880 (14.7 MP)
- UHD 8K — 7680×4320 (33.18 MP)
Note the loose "2K" usage — it sometimes means 1080p (because 1920 ≈ 2000) and sometimes means QHD 1440p. Always check pixel dimensions when accuracy matters.