Sure, Adobe Photoshop has a batch conversion tool buried within its menus, but even then some people might not find it to be the easiest means of doing batch image conversions. One of the key things it lacks is the ability to batch re-size images using a specified single dimension of either width or height and locking the batch of images to their original aspect ratio through proportionally automatically re-sizing the other dimension of the image. Meaning that all the images that you want to batch re-size have to be pre-cropped to the same size beforehand. I haven't really used it since the days when the popularity of mini disc as a format was peaking within the general consumer domain. 

Obviously this feature is included for single re-size  jobs in Adobe Photoshop, but its generally vastly quicker (near instant on my machine) to do it with the default MS paint app if you're browsing thumbnails from explorer or Adobe Bridge and want to re-size single images with a constrained aspect ratio through altering a single dimension of an image.

Fortunately there's a free batch conversion app for that called Fast Stone Viewer which I just found having decided I've had enough of having to painstakingly re-size hundreds of images one by one using MS paint and generally being very suspicious of free third part apps that install themselves on my computer and make registry alterations. In fact from initial testing it seems to be vastly faster then Adobe bridge too as far as load time, image previewing, and preliminary image tweaking features are concerned. If that wasn't enough, you might also like to know that it comes in a very convenient portable flavor too that doesn't permanently install or write anything to your computers registry, it saves all its settings that you make for the app in a file within the folder that you're running it from. Most importantly of all it has the ability of batch image re-sizing with the maintenance of aspect ratio through specifying an arbitrary single dimension size of either width or height.

You can get it here.