✂️ Photo Aspect Ratio Cropping Calculator
Enter your original image dimensions and a target aspect ratio to calculate the largest crop that fits within your image.
Which edge gets trimmed
The tool compares your image's ratio with the target and keeps whichever dimension is already the tighter fit, so nothing is ever invented or upscaled:
target = a / b
if w/h > target: crop = (h × target) × h keep the height, trim the sides
else: crop = w × (w / target) keep the width, trim top and bottom
centre offset = ((w - cropW) / 2, (h - cropH) / 2)A 4000 × 3000 file is 1.333 wide, narrower than 16:9's 1.778, so the width survives and the height is cut: 4000 × 2250, with 3,000,000 pixels trimmed. Ask for 1:1 instead and the comparison flips - the height is the limit, giving 3000 × 3000.
The five targets on a 4000 x 3000 frame
| Ratio | Used for | Crop | Kept |
|---|---|---|---|
| 1:1 | square posts | 3000 × 3000 | 75% |
| 4:5 | portrait feed | 2400 × 3000 | 60% |
| 16:9 | video, screens | 4000 × 2250 | 75% |
| 3:2 | 6x4 prints | 4000 × 2667 | 89% |
| 2:3 | upright prints | 2000 × 3000 | 50% |
Only the size comes back, not the position. For a centred crop, offset by half the difference: 4:5 out of a 4000 px wide frame starts at x = 800.
Frequently asked questions
How do I crop a 4:3 photo to 16:9?
Take the full 4000 px width and cut the height to 2250 px, losing 750 px - a quarter of the frame. Decide first whether the sky or the foreground goes, because a 16:9 crop from 4:3 is a big bite.
Why does 4:5 throw away so much?
Because 4:5 is taller than a landscape frame is shaped, so the cut comes off the sides: 4000 px of width becomes 2400. You keep 60% of the pixels. Shoot the frame upright if the picture is destined for a portrait feed.
Does cropping reduce image quality?
It removes pixels rather than degrading them. A 12 MP frame cropped to 16:9 is a 9 MP file - 4000 x 2250 px, which still prints 13 x 7.5 inches at 300 dpi.