How to Turn an 8-by-10 Into a Poster Size

Open the photo-editing program you typically use to edit your pictures. Provided your photo editor allows you to crop, adjusting the image size and DPI of your picture will work for this process. If your photo editor does not do this, consider downloading Adobe Photoshop or GIMP, which is modeled on Photoshop.

Click "File" and select "Open" from the drop-down menu. Navigate to the folder containing the image you want to enlarge to poster size. Click the file to highlight the image and click "OK" to open the image in your editor.

Click the "Crop" tool and select an image size of 8-by-12 inches and keep the dots per inch at the same value it is presently. An 8-by-10 image has a ratio of 4:3 a 24-by-36 image has a 16:9 ratio and you need to adjust the ratio of the image before enlarging it. This will require you to crop the image resulting in some of the image being trimmed from the 8-by-10 ratio so you can enlarge the image. When you set the crop size to 8-by-12 and crop the picture, the resulting picture will be in the correct ratio to enlarge the image to 24-by-36 inches.

Click "Image" in the navigation bar and select image size from the drop-down menu. Change the DPI from its current value to 220. When you print an 8-by-10 image you want a higher resolution as you will view the image close up. Viewing a poster will be done at a further distance allowing you to use a lesser DPI. Change the height and width dimensions to 24-by-36 inches and click "OK" and the program will adjust the size of the image.

Click "File" in the navigation bar and select "Save As," give your enlarged image a new name and save it to your home computer.