400x400 pixels is the recommended profile picture size for Twitter (X) and LinkedIn. Both platforms accept images at this dimension and display them as circular crops. Uploading at exactly 400x400 ensures maximum quality for your profile picture.
The 400x400 size provides enough resolution for sharp display on both standard and retina screens. At 2x pixel density, this means the image appears crisp on displays up to 200x200 CSS pixels.
With ImgTools, upload your photo, crop to a 1:1 square centering your face, and resize to 400x400. Remember that platforms will apply a circular mask, so keep the subject centered within a circle inscribed in the square.
Save as JPEG at 90% quality. The file will be small (15-30KB) at this dimension.
All processing happens locally in your browser.