Changing your image size
Changing the size of an image in Pixlr Editor is easy. With an open image, choose Image > Image Size and alter the image size by entering a desired size or using the built-in sliders. If you want your image to have the same proportions after resizing (most likely yes if you are editing photographs you've taken) you'll want to make sure the "constrain proportions" option is checked. In this option, you increase the height or length and Pixlr will compute the rest. Not using constrain proportions means your image may look "stretched" after resizing.
Note: Canvas size is different than image size
You can also alter the size of your canvas. The canvas is the "Background" layer that every new image opened in Pixlr rests on. It's your working space, and you can make it as large as you like. Your image won't be affected. You can also rotate your canvas or flip it horizontally or vertically. Note that there is a 4,000 pixel limit to the height or width of any image.
Note also that when you change your canvas size, there is no option to constrain proportions because you won't be changing the image itself but the canvas upon which it rests. Also note that you can choose where the image will be anchored when your canvas size changes. Here, for example, my image will end up in the bottom right hand corner of my newly sized canvas:
Free transform: quick and easy resizing
You can also use the free transform feature to resize layers. You won't have the same level of control over the specific size, but this is a quick and easy way to resize an image. Choose Edit > Free transform and drag the blue corner indicators around until the image is about the right size.
Want to quick resize but maintain the same proportions? Hold down the Shift key while resizing.
Rotating an image or layer
The corners also sport a rotation option, which lets you rotate or tilt your image by hand. Just mouse over the corners to see the rotate option as shown in the image below. One important detail to consider is that text can not be rotated in this way unless you first rasterize the text, which turns your text into a layer that is an image (and no longer text).
There is no grid (gridlines) or ruler in Pixlr Editor at this time, but it's a popular request from users that we hope to implement in the future. With no grid, there is also no ruler to measure in inches.