Aspect Ratio Calculator
Aspect ratio describes the proportional relationship between an image or screen's width and height, expressed as two numbers separated by a colon (e.g., 16:9). This calculator simplifies any pair of dimensions to their lowest-term ratio by dividing both values by their greatest common divisor (GCD), so 1920×1080 reduces to 16:9 and 2560×1440 reduces to 16:9 as well.
You can also work in reverse: enter a known aspect ratio and one dimension to instantly calculate the matching second dimension. This is essential for maintaining visual proportions when resizing images, designing layouts, or configuring video output — for example, finding the correct height for a 16:9 banner that is 1200 px wide.
How it works
To simplify W:H, compute GCD(W, H) then divide: simplified ratio = (W/GCD) : (H/GCD). To scale: given ratio R_w:R_h and a known width W, height = W × (R_h / R_w). Given a known height H, width = H × (R_w / R_h).
Use cases
- Finding the simplified aspect ratio of a photo or video (e.g., 1920×1080 → 16:9)
- Calculating the correct height for a responsive banner or thumbnail at a given width
- Ensuring consistent proportions when resizing graphics for different platforms
- Determining the exact pixel dimensions for widescreen, square, or portrait video formats
- Verifying that cropped or scaled images maintain the intended aspect ratio
Frequently asked questions
What is the aspect ratio of 1920x1080?
1920×1080 simplifies to 16:9. The greatest common divisor of 1920 and 1080 is 120, and 1920 ÷ 120 = 16 while 1080 ÷ 120 = 9. The same 16:9 ratio applies to 1280×720, 2560×1440, and 3840×2160 (4K UHD).
How do I calculate the aspect ratio from width and height?
Divide both dimensions by their greatest common divisor (GCD). For 1440×900, the GCD is 180, so the ratio is 8:5 (equivalent to 16:10). This calculator finds the GCD automatically and shows the reduced ratio instantly.
What are the most common aspect ratios?
16:9 dominates HD video, monitors, and TVs; 4:3 was standard for older displays; 21:9 is used by ultrawide monitors; 1:1 is the square format; and 9:16 is vertical video for Stories, Reels, and TikTok. Photography often uses 3:2, the classic 35 mm film ratio.
How do I find the height for a 16:9 image at a given width?
Multiply the width by 9/16. A 1200 px wide 16:9 banner needs a height of 1200 × 9 ÷ 16 = 675 px. In general, height = width × (ratio height ÷ ratio width), which is exactly what the scaling mode of this calculator does.
What is the difference between 16:9 and 16:10?
A 16:10 display is slightly taller than 16:9 at the same width — for example 1920×1200 versus 1920×1080. 16:10 (also written 8:5) is common on productivity laptops, while 16:9 is the standard for video content, so 16:9 footage shows small letterbox bars on a 16:10 screen.