1. ISO 216 Standard (International): Used in most countries worldwide (Europe, Asia, Africa, etc.), based on a √2 aspect ratio (1:1.4142).
2. ANSI/ARCH Series (North America): Used in the US, Canada, and Mexico, defined by ANSI/ASME Y14.1.
3. Regional Standards: Japanese B Series (JIS B), Chinese Standards.
4. Specialty Sizes. RA & SRA Series (ISO 217), Business Cards.

1. Small Prints (Snapshots & Casual Use).
Sizes: 2 × 2 inches (Passport photos); 3.5 × 5 inches (Standard snapshot); 4 × 6 inches (Most common photo print).
2. B. Medium Prints (Framing & Display).
Sizes: 5 × 7 inches (Common for portraits); 8 × 10 inches (Popular for framing); 8.5 × 11 inches (Letter size, photo books).
3. Large Prints (Wall Art & Professional Use).
Sizes: 11 × 14 inches (Gallery-style prints); 16 × 20 inches (Poster size); 18 × 24 inches (Large posters, canvas).
4. Extra-Large Prints (Commercial & Decorative).
Sizes: 20 × 30 inches (Poster, canvas wrap); 24 × 36 inches (Movie poster size); 30 × 40 inches+ (Billboards, murals).

A general rule is that your viewing distance should be about 1.5 to 2.5 times the diagonal screen size of the TV for an optimal experience.
For 1080p TVs: Sitting too close may reveal pixelation.
For 4K TVs: You can sit closer (~1–1.5x screen height) without losing clarity due to higher resolution.
For 8K TVs: You can sit even closer (~0.75x screen height).

1. Facebook Profile Picture: 170×170px (displays 170×170 on desktop, 128×128 on mobile).
2. Instagram Profile Picture: 320×320px (displays 110×110).
3. Twitter/X Profile Picture: 400×400px (displays 200×200).
4. LinkedIn Profile Picture: 400×400px (displays 300×300).
5. Pinterest Profile Picture: 165×165px (displays circular).
6. TikTok Profile Photo: 200×200px (20KB max).