The Ultimate Twitter and Facebook Image Template for Advertisers
If you're planning to advertise (or promote) your Facebook posts, there are additional restrictions you need to follow to keep Facebook from rejecting your ads. The biggest of these is the 20% text restriction.
Although this limit is listed in Facebook's requirements, they don't explain how they calculate it. To calculate the text percentage, Facebook draws a 5x5 grid over the portion of the ad visible in the timeline view. If text covers any portion of a square, the whole square is counted. If your text covers more than 5 squares, your ad will likely be rejected.
To make sure my ads are compliant, I've created a PSD with guides dividing the center portion of the image into a 5x5 grid which you can download here. If you make sure your text only covers 5 blocks, you shouldn't have any problems with ad rejection.
Note: I recommend setting the template file to “Read-Only” to keep you from accidentally saving over it. Once you’ve made your changes, just make sure to click “Save As.”