An A4 document measures 210 x 297 mm. Translating these dimensions into pixels requires setting a resolution, expressed in pixels per inch (ppi). Without this parameter, the number of pixels in an A4 file means nothing. Choosing the right combination of resolution and usage prevents the creation of unnecessarily large files or, conversely, files that are too low in quality to be printed correctly.
Resolution and Resampling: What Really Increases the Size of an A4 File
The most common confusion is believing that increasing the resolution of an image automatically improves its quality. In software like Photoshop, the relationship is direct: physical dimensions = pixel dimensions divided by resolution. Changing the ppi setting without enabling resampling does not change the number of pixels in the file. The file size remains the same.
Resampling is the true factor of overhead. When it is enabled, the software adds or removes pixels to reach the new target resolution. Each operation of this type modifies the color data and increases (or degrades) the file. Adobe recommends avoiding enlargement when possible and resampling only once, as repeated adjustments progressively degrade quality.
Before resizing an image for A4 media, it is essential to check if the existing pixel count already meets the need. A detailed guide on A4 dimensions in px on SAV 35 explains how far to go in definition without unnecessarily increasing the file size.
A4 Pixels by Resolution: Comparative Table by Usage
The number of pixels in an A4 document varies significantly depending on the chosen resolution. Three levels cover almost all common cases.
| Usage | Resolution | Pixels (width x height) |
|---|---|---|
| Screen display, email | 72 ppi | 595 x 842 |
| Mixed use, print draft | 150 ppi | 1240 x 1754 |
| Quality printing (flyer, photo, poster) | 300 ppi | 2480 x 3508 |
Moving from 72 to 300 ppi multiplies the number of pixels by more than sixteen. For an uncompressed color image, the file size follows the same progression. An A4 at 300 ppi in RGB colors weighs significantly more than an A4 at 72 ppi, even though the display on screen shows no perceptible difference.
How to Read This Table in Practice
A flyer intended for professional printing requires 300 ppi. An image included in a slideshow or sent via email has no reason to exceed 150 ppi, or even 72 ppi if the target screen remains a standard monitor.
The screen resolution does not automatically justify 300 ppi. For strictly digital use, changing the resolution without resampling does not change the file size. The ppi setting only affects the physical display or print size, not the actual amount of data.
A4 File Format: JPEG, PNG, WebP, or Vector
The choice of file format weighs as heavily as the resolution on the final file size. A raster image records color data for each pixel. The more pixels there are, the larger the file, but the compression format can largely offset this burden.
- The JPEG applies lossy compression: each save slightly degrades the data, but the file remains compact. Suitable for photos and complex visuals intended for print or web.
- The PNG retains all data (lossless compression). The file can be significantly larger than a JPEG for a photo but remains relevant for images with transparency or sharp text.
- The WebP and AVIF formats allow for a separation of visual quality and file size. They offer more efficient compression than JPEG at equivalent perceived quality, making them a relevant choice for digital media.
- For a logo, diagram, or simple text, a vector format (SVG, vector PDF) is generally more suitable: it remains resizable without loss and can be lighter than an equivalent raster image.
A print medium like a business card or A4 flyer will be saved in high-quality JPEG or PDF. A web visual on a product page will benefit from being exported in WebP to reduce loading time without sacrificing sharpness.
Adapting A4 Resolution to the Final Medium: Mistakes to Avoid
The classic pitfall is preparing all files at 300 ppi by default, regardless of use. An A4 document intended solely for digital display (presentation, PDF viewed on screen, image embedded in a website) does not need this density. Producing a 300 ppi A4 for screen use wastes storage space and slows loading without providing any visual gain.
Three Reflexes Before Exporting
- Check the existing pixel count in the source file before any modifications. If the image already covers the target size, simply adjust the ppi setting without resampling.
- Resample only once. Successive enlargements stack artifacts and increase the file size without improving actual quality.
- Choose the export format based on the distribution channel: JPEG or PDF for print, WebP for the web, vector for logos and diagrams.
A well-sized file from the start requires no resolution adjustments. When the original photo is taken with a sufficiently defined sensor, the pixel count easily covers an A4 print at 300 ppi. The work then consists of cropping and exporting in the right format, not artificially inflating the resolution.
The pixel size of an A4 is not a fixed value. It depends on the intended medium, the file format, and the care taken to avoid unnecessary resampling. Keeping the file as light as possible for each channel remains the best guarantee of quality and speed, both on screen and in print.
