How to use the Aspect Ratio Calculator
- Enter the original size or ratio. Type the width and height of your image or artwork under Original size or ratio — pixels, inches or plain numbers like 4 and 5. Or tap one of the Presets, from 1:1 to the golden ratio.
- Read the ratio. The card shows the simplified ratio, the decimal version, whether the piece is portrait or landscape, and the closest familiar ratio with how far off it is.
- Scale it. Under New size, same ratio, type the width you need and the height appears (or the other way round). The calculated box is tinted so you always know which number is the answer. Untick Round to whole numbers if you work in inches or centimeters.
- Test a crop. Pick a format in Put it in a frame of to see two previews side by side: cropping to fill that shape, and fitting the whole image inside it with borders. Each shows the exact percentage you keep.
- Copy what you need. Copy CSS aspect-ratio gives you a ready line for a portfolio site; Copy summary copies the ratio, the new size and the crop numbers as plain text.
The math behind scaling without distortion
An aspect ratio is simply width divided by height. A 3000 × 4500 pixel scan has a ratio of 0.6667, which simplifies to 2:3 because both sides divide by 1500. Any size with the same quotient keeps the same shape, so the missing side is one multiplication away:
- new height = new width × (original height ÷ original width)
- new width = new height × (original width ÷ original height)
At 1080 pixels wide, that 2:3 scan becomes 1080 × 1.5 = 1620 pixels tall. Scale it to 36% and nothing stretches, because both sides shrank by the same factor.
Simplifying matters because ratios hide inside awkward numbers. A 1366 × 768 screen reduces to 683:384, which looks random until you notice it sits 0.05% away from 16:9. An A4 page scanned at 300 DPI is 2480 × 3508 pixels, or 620:877 — the 1:√2 shape of every A-series sheet, rounded to whole pixels. That √2 is the reason A-series paper works the way it does: fold A4 in half and you get A5 in exactly the same proportions, something no other ratio can do.
The golden ratio, about 1:1.618, has a similar self-similar trick: cut a square off a golden rectangle and the leftover piece is another golden rectangle. It’s a pleasant proportion rather than a rule — plenty of great paintings ignore it — but it’s there in the presets for when a client asks. For spirals and section lines, use the Golden Ratio Calculator.
What a crop really costs
Moving artwork between formats means either cropping (losing part of the image) or fitting (adding borders). The numbers below are the share of your image that survives a centered crop to fill the target shape — the same figure the left-hand preview shows.
| From | To | Image kept | Typical situation |
|---|---|---|---|
| 4:5 | 11:14 | 98.2% | 8×10 print shown in an 11×14 frame |
| 3:4 | 1:√2 | 94.3% | 18×24 canvas photographed for an A4 portfolio page |
| 3:4 | 4:5 | 93.8% | phone photo of a painting posted at 4:5 |
| 5:7 | 4:5 | 89.3% | 5×7 card design reused as an 8×10 print |
| 2:3 | 3:4 | 88.9% | 24×36 poster file sent to an 18×24 frame |
| 1:√2 | 4:5 | 88.4% | A4 drawing sold as an 8×10 print |
| 2:3 | 4:5 | 83.3% | 12×18 photo cropped to 16×20 |
| 2:3 | 1:1 | 66.7% | portrait painting in a square grid tile |
| 16:9 | 1:1 | 56.3% | video still turned into a square post |
Anything above about 95% is usually invisible. Below 90%, check the edges: a signature in the corner or a hand near the frame edge is exactly what goes first. Below 70%, crop by hand rather than letting software center it for you.
Tips from practice
Pick the final ratio before the first sketch. If a piece is destined for a 16 × 20 in canvas, draw your thumbnails in a 4:5 box. Composing in 2:3 and squeezing into 4:5 later costs you a sixth of the picture, as the table shows.
Round once, at the very end. Each rounding nudges the ratio slightly. Scale from the original numbers every time rather than resizing a resized file, and keep decimals until you type the final pixel size.
Fit with a border when the edges matter. For artwork, a white or colored border usually beats a crop. A 2:3 piece fitted into 4:5 fills 83.3% of the frame and loses nothing — and an even border reads as a deliberate mat.
Leave room for a mat or bleed. If a print will be matted, or a printer asks for 3 mm (⅛ in) of bleed, those margins can change the effective ratio. Work out the print size first with the DPI & Print Size Calculator, then check the ratio of the visible window.
Use CSS instead of fixed heights on your site. A line like aspect-ratio: 4 / 5; on a gallery thumbnail, together with object-fit: cover, crops every image to the same shape without editing a single file — handy when your portfolio mixes canvases of different proportions.