Image Calculators — DPI Pixels Print Size Aspect Ratio and File Size
Calculate DPI pixels to inches and centimeters print size aspect ratio megapixels and file size for any image. Instant results that run privately in your browser.
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Last updated 25 August 2026
Get the numbers right before you export
Every print and upload has a number attached, and getting it wrong means wasted ink, a distorted layout or a file rejected by a form. These calculators turn width, height, resolution and target size into exact numbers so you know before you export whether a photo fits a 4 by 6 frame, a portal limit or a platform ratio. Enter any two values and the result updates instantly, which removes the guesswork from resizing and compressing. Use the print size calculator for physical prints and the image file size calculator to estimate bytes before you save.
Print and screen math explained
Pixels divided by DPI gives inches, the rule behind every print size on this site. At 300 DPI a 4 by 6 print is 1200 by 1800, an 8 by 10 is 2400 by 3000, and a US passport photo is 600 by 600. Drop to 150 DPI and the same print needs half the pixels, which is fine for posters viewed from a distance. For screens the same math works without DPI, since a 1920 by 1080 frame is full HD at a 16 by 9 ratio. If you need the full table of standard sizes in one place, the photo print size chart guide lists them all.
Aspect ratio and megapixels
Aspect ratio locks the proportions of an image so a resize never stretches it. The ratio is width divided by height, reduced to its simplest form, so 1920 by 1080 becomes 16 by 9 and 1080 by 1080 becomes 1 by 1. Megapixels is width times height in millions, which correlates with how much detail the file holds, so a 12 megapixel camera produces 4000 by 3000 pixels. Use the aspect ratio calculator to map one ratio to another, like 4 by 3 to 16 by 9, or to find the height that matches a chosen width without distortion.
File size planning
Estimated file size depends on pixels, color depth, compression and quality, so the same dimensions can produce very different byte counts across JPG, PNG and WebP. A photographic JPG at balanced quality sits far below the raw pixel figure, while a PNG keeps more data because it is lossless. The image file size calculator gives a close estimate before you export, and the file size converter translates KB to MB for portal limits. When a form forces an exact cap, such as 1MB, pair the estimate with a target size compressor so the final file fits at the best quality the limit allows.
Instant private math
Every calculator updates as you type and runs entirely in your browser, so no form is submitted and no data is collected. Check a print size, convert pixels to centimeters or estimate bytes on the spot, then continue to the resizer or compressor that matches the result. Because the math is instant, you can compare several DPI settings or aspect ratios in seconds without opening another app or re-entering your image. The values work with the rest of the site, so a DPI result flows straight into the resize and compress steps. For the theory behind formats and file weights, the image formats explained guide is a useful companion.
- Aspect Ratio Calculator — Find Ratio from Pixels FreeReduce any width by height to its simplest ratio, like 1920 by 1080 to 16 by 9, for video, images and responsive design. The calculation runs instantly in your browser, so you can check any resolution without entering values anywhere else.Open tool
- DPI Calculator — Pixels to Print Size Free OnlineConvert between pixels, DPI and physical print size, which is essential for printing and scanning. Enter any two values and the calculator fills in the third instantly, all locally in your browser.Open tool
- Pixels to Inches — Convert PX to Inches Free OnlineConvert pixel dimensions to physical inches at any DPI, which is essential for print sizing and layout. Enter the pixel width and the DPI, and the calculator shows the inch size instantly without uploading anything.Open tool
- Pixels to CM — Convert PX to Centimeters Free OnlineConvert pixel dimensions to centimeters at any DPI, the metric equivalent for print design. Enter the pixels and DPI, and the calculator returns the size in centimeters instantly, all locally on your device.Open tool
- Print Size Calculator — Max Print Size Free OnlineFind the largest quality print size for a given pixel resolution and DPI target, so you never pay for a soft or pixelated enlargement. Enter your pixel dimensions and the calculator returns the printable inches instantly, all locally.Open tool
- Image File Size Calculator — Estimate Bytes Free OnlineEstimate the raw or compressed file size of an image before you create it, so you can plan uploads and storage. Enter dimensions and format details, and the estimate updates instantly, all in your browser.Open tool
- Megapixel Calculator — Pixels to Megapixels Free OnlineTurn any pixel width and height into a megapixel count, the standard spec for cameras and sensors. Enter the dimensions and the calculator returns the megapixels instantly, so you can compare camera resolutions.Open tool
- File Size Converter — KB to MB and GB Free OnlineConvert any storage size between B, KB, MB and GB, so you can interpret download and upload limits correctly. Enter a value in one unit and the converter returns every other unit instantly, all in your browser.Open tool
Frequently asked questions
How many pixels do I need for a sharp 4 by 6 print at 300 DPI
1200 by 1800 pixels. At 300 dots per inch, width is pixels divided by DPI, so 1200 divided by 300 equals 4 inches and 1800 divided by 300 equals 6 inches. For an 8 by 10 print at 300 DPI you need 2400 by 3000 pixels. The print size calculator works in both directions.
How do I convert pixels to inches or centimeters for printing
Use the pixels to inches or pixels to cm calculator and enter the DPI. It divides the pixel count by the resolution to show the physical size. If you know the print size you want instead, use the print size calculator to work backward to the required pixels and DPI in one step.
What aspect ratio should I use for a 1920 by 1080 video thumbnail
16 by 9. The width divided by height equals 1.78, and reducing the ratio gives 16 by 9. Use the aspect ratio calculator to convert any width to its matching height for this ratio before you resize, so video thumbnails and frames keep clean proportions.
Why does DPI matter for print but not for screens
DPI describes how many pixels map to one inch of paper, so printers need it to set physical size. Screens show pixels directly, which is why display size depends on pixel dimensions, not DPI. A 1920 by 1080 image is full HD on screen at any DPI value. Check your numbers with the DPI calculator.
How do I estimate file size before exporting JPG or WebP
Open the image file size calculator, enter the dimensions and expected quality or bits per pixel, and it estimates the byte count. Compare that estimate to a target like 500KB, then use a target size compressor to hit the closest quality that fits under the limit.
Which calculator helps me meet a portal upload limit of 1MB
Use the image file size calculator to estimate the current size, then open compress image to 1MB. The target size compressor searches for the highest quality that still fits under 1MB, runs in your browser, and can process several files at once.
How do I calculate the file size of an image from its pixels
Multiply width by height to get total pixels, multiply by bits per pixel, then divide by 8 to get bytes before accounting for compression. JPG and WebP compress far below the raw figure, while PNG stays closer to it. The image file size calculator handles all of this for you.