FastStone Photo Resizer allows you to resize, convert and rename photos in batch mode. This means that you can process a large number of photos in one single operation.
To resize images, you need to select the folder or desired images, then choose Batch Convert. Here, you can convert them to another format or not, but also you can set resize options.
You can set the new size in pixels, percentage or based on one side (width or height). You can enter the new size manually or choose one from the presets. It has options to preserve aspect ratio, do not resize if the image is smaller, switch with and height.
Furthermore, while resizing, you can set options to change colors, rotate, crop and other effects.
FastStone Photo Resizer is available as free download for Windows 32-bit and 64-bit.