1. The Quilter's Little Helper by Robert Kaufman
I love this app because it does all the quilting math work for you, which is great for me because I'm pretty much math challenged.
It has several calculations, but my favourites are: backing and batting measurements, binding yardage needed, and piece count (calculates the number of pieces you can cut from a larger piece of fabric).
2. Quick & Easy Quilt Block Tool by C&T Publishing, Inc.
This app is great if you need a specific size for one of the basic blocks. It gives you the cutting measurements for 201 blocks in 5 different sizes. It also has a guide for basic cutting and sewing methods.
3. How Much Thread by Superior Threads
Just like it says, this app calculates the amount of thread you'll need for your quilt project. It only provides measurements for the average bed sizes, so you can't calculate for your own specific project if it's not a bed, i.e wall quilts. You could, however, use a bed size that is closest to your project size and go from there. Also, you have to remember to double your amount calculated for the bobbin thread.
4. Colour Wheel by Google Play
I love this app. I recently posted information on colour theory for quilters and this would be a good companion app for that. You can get your quilt colours by setting the combination you want to use, i.e. triad, and pointing your "pie" at the main colour you want to use in that combination. For example, let's say your main colour is red and you want a triad combination for red. Using the drop down menu, select Triad. Then, turn your pie to point at red and all the triad colours will appear on the top. This app is very user-friendly and you get your results in seconds.