If this tool helped you, you can buy us a coffee ☕
选择常见照片/纸张尺寸并指定DPI,快速换算为像素宽高,适合打印、设计排版。
JSON to Protobuf Converter
Free online JSON to Protobuf converter. Instantly generate Protocol Buffers message definitions from JSON data.

Pixel to Millimeter Converter
根据PPI密度,将像素和毫米相互转换,支持自定义密度值,适用于UI设计和印刷排版。

PX to REM Converter
A bidirectional PX to REM converter for front-end developers and designers, featuring customizable root font sizes.
A 4×6 inch photo requires 1200×1800 pixels for clear printing at 300 DPI. Pixels are the smallest color blocks in a digital image, and DPI (dots per inch) determines the density of these blocks when printed. The formula is simple: Pixels = Size in Inches × DPI. Tell the calculator the physical size of the photo paper and set your desired DPI, and it will calculate how many pixels your image needs. This tool features dozens of common sizes like 1-inch, 2-inch, 5-inch, 6-inch, and A4. It automatically converts millimeters and centimeters to inches. Just select the size, enter the DPI, and the pixel width and height will instantly appear on the right.
You plan to print a standard 4×6 inch family photo, and the print shop requires "300 DPI, minimum 1200×1800 pixels." How do you confirm this?
Select "6-inch (4×6 inches)" from the calculator's size dropdown menu. Enter 300 in the DPI input box. The calculator displays: Width 1200 px, Height 1800 px. This result comes exactly from 4 inches × 300 and 6 inches × 300: 4″ × 300 = 1200 px, 6″ × 300 = 1800 px. This means your digital photo must be at least 1200×1800 pixels for the printed 4×6 photo to be sharp and clear. If your original phone photo is only 800×1200 pixels, the printed image will appear pixelated or blurry. In this case, you either have to accept lower clarity or print at a smaller size.
2-inch ID photo: Applying for a passport requires a 2-inch bareheaded photo, and many photo studios ask for a digital version at 413×579 pixels. Where does this come from? Select "2-inch (35×49 mm)" in the tool and set the DPI to 300. 35 mm ÷ 25.4 ≈ 1.378 inches, and 49 mm ÷ 25.4 ≈ 1.929 inches. Multiplying these by 300 gives ≈ 413 px and 579 px, respectively. Crop your photo to these exact pixel dimensions before submitting, and the size will be perfectly accurate.
The same photo on a webpage: For the same 4×6 inch image, if it's just for a personal blog, you don't need 300 DPI. Keep the size at "6-inch (4×6 inches)" and change the DPI to 72. The calculator outputs 288×432 px. This pixel size looks clear on a screen, and the file size is much smaller, allowing for faster loading.
Comparing the two examples: For the same physical size, dropping the DPI from 300 to 72 reduces the total required pixels from 2.16 million to about 120,000—a difference of an order of magnitude. Choosing the right DPI directly determines whether your image file is "just right" or "wasted space."
The width and height pixels provided by the calculator represent the "digital size" your image needs to achieve.
A simple rule of thumb: For printing, aim for "no less than"; for screens, aim for "just enough."
ID photo creation: When students or professionals apply for various IDs, they are often asked for a "1-inch white background 295×413 pixels" or "2-inch blue background 413×579 pixels" photo. By selecting the size and setting the DPI in this calculator, you'll know exactly what pixel dimensions to crop your photo to, avoiding the hassle of retaking it.
Online photo printing orders: When uploading photos to a printing website, the system usually prompts "Recommended pixels XXXX×XXXX." If you're unsure whether your original photo is large enough, you can use the calculator to match your chosen print size and DPI. Confirm the dimensions before uploading to reduce rejected orders.
Poster and brochure layout: When designers create a new canvas in Photoshop or Illustrator, they need to calculate the pixel width and height based on the final print size and DPI. For instance, for a single A4 brochure page (210×297 mm) at 300 DPI, the tool instantly provides 2480×3508 px, which can be used directly as the dimensions for the new file.