# SizeKit

> Fast size references and calculators for paper sizes, screen resolutions, photo print sizes, social/web image sizes, DPI, pixels, and aspect ratios.

SizeKit is static-first and answer-first. Pages show direct dimensions before custom calculators so search engines, answer engines, and users can extract the important value quickly.

## Primary References
- [SizeKit](https://sizekit.online/): Fast size references and calculators for paper, screens, print, pixels, DPI, aspect ratios, and social images.
- [Paper Sizes](https://sizekit.online/paper-sizes): Flat directory of paper, envelope, card, regional, and photo-print size pages.
- [Screen Sizes](https://sizekit.online/screen-sizes): Flat directory of iPhone, Samsung, Huawei, Android, iPad, MacBook, tablet, and PC screen sizes.
- [Photo & Print Sizes](https://sizekit.online/photo-print-sizes): Common photo print and ID-photo sizes in inches, millimeters, and 300 DPI pixels.
- [Social & Web Sizes](https://sizekit.online/social-media-image-sizes): Social and web image sizes for Xiaohongshu, TikTok, Douyin, WeChat, Bilibili, Instagram, YouTube, Open Graph, and more.
- [DPI Calculator](https://sizekit.online/dpi-calculator): Convert physical size and DPI to pixels, pixels and DPI to print size, or pixels and physical size to actual DPI.
- [Print Size Calculator](https://sizekit.online/print-size-calculator): Convert image pixel dimensions and DPI into printable inches, centimeters, and millimeters.
- [Aspect Ratio Calculator](https://sizekit.online/aspect-ratio-calculator): Simplify ratios and scale width or height without changing proportions.

## High-Intent Answer Pages
- [A4 Size](https://sizekit.online/a4-size): A4 is 210 x 297 mm, 8.27 x 11.69 in, and 2480 x 3508 px at 300 DPI.
- [US Letter Size](https://sizekit.online/letter-size): US Letter is 215.9 x 279.4 mm, 8.5 x 11 in, and 2550 x 3300 px at 300 DPI.
- [A4 Size in Pixels](https://sizekit.online/a4-size-in-pixels): A4 pixel presets at 72, 96, 150, 300, and 600 DPI; 300 DPI is 2480 x 3508 px.
- [Xiaohongshu Note Cover Size](https://sizekit.online/xiaohongshu-note-cover-size): Xiaohongshu Note Cover is 1080 x 1440 px, ratio 3:4, last reviewed 2026-05.
- [TikTok Video Size](https://sizekit.online/tiktok-video-size): TikTok Video is 1080 x 1920 px, ratio 9:16, last reviewed 2026-05.
- [Douyin Video Cover Size](https://sizekit.online/douyin-video-cover-size): Douyin Video Cover is 1080 x 1920 px, ratio 9:16, last reviewed 2026-05.
- [WeChat Official Account Cover Size](https://sizekit.online/wechat-official-cover-size): WeChat Official Account Cover is 900 x 383 px, ratio 2.35:1, last reviewed 2026-05.
- [iPhone 17 Pro Max Screen Size](https://sizekit.online/screen-sizes/iphone-17-pro-max): iPhone 17 Pro Max screen size is 1320 x 2868 px with a 19.5:9 aspect ratio.
- [Galaxy S25 Ultra Screen Size](https://sizekit.online/screen-sizes/galaxy-s25-ultra): Galaxy S25 Ultra screen size is 1440 x 3120 px with a 19.5:9 aspect ratio.
- [Google Pixel 9 Screen Size](https://sizekit.online/screen-sizes/pixel-9): Google Pixel 9 screen size is 1080 x 2424 px with a 20:9 aspect ratio.
- [PC Screen Sizes](https://sizekit.online/pc-screen-sizes): Common laptop, monitor, ultrawide, 4K, 5K, and 6K resolutions.

## Data Coverage
- Paper/detail records: 107
- Screen-size records: 95
- Social/web image records: 68
- Social filter categories: 13
- DPI presets: 72, 96, 150, 300, 600
- Last site generation review: 2026-05-28

## Important Formulas
- inch = millimeters / 25.4
- pixels = round(inches x DPI)
- DPI = pixels / inches
- aspect ratio = width:height simplified by greatest common divisor

## Complete Index
- [Full SizeKit page index](https://sizekit.online/llms-full.txt): every generated page with a short machine-readable summary.