Open the Photo Dimensions Calculator — Free Image Size & Aspect Ratio in your browser and click the blue "Choose file" button or drag your image onto the drop area; you can also paste an image from the clipboard into the input field. The tool immediately reads the file and displays its pixel dimensions (e.g., 4000 x 3000 px), file type, and orientation, then shows a simplified aspect ratio (e.g., 4:3) and the greatest-common-divisor ratio. To resize, enter the new width or height in the fields, pick units (pixels, inches, cm), choose whether to "Maintain aspect ratio" and press the "Calculate" or "Resize image" button to get exact output dimensions and the download link.