First the block size you have. That's 8" if you're using one of the free paper pieced blocks that Vicki located here. Now anyone for anyone wondering; the text on those background curves says in German, spilt to fit on paper, it doesn't really need split there.
For my Lone Star I needed my background blocks to finish at 23.5". That means sewn in at 23.5", which is an off measurement but certainly something we can easily work with.
Let's punch that into a Calculator. 23.5" Divided by 8 equals 2.9375. Good.
Now just change that into a percentage. 2.9375 move the decimal point right two places and add a % sign to the end 293.75%. The block needs to increase 293.75% Most places can't increase by a fraction of a percent so we'll round the .75 up to 294%.
Now it's just a simple case of printing out your paper pieced block and taking it to a copy place or a blue print place and have them make the enlargement.
When you get your enlargement back you'll notice that your 1/4" seam allowance marks are now huge, but that's okay. Just use your templates and rulers to draw the offset line by drawing your exterior line 1/4" outside of the block and ignore the printed seam allowance marks in favor of the ones you just made.
You're all set, see that wasn't so bad. If you're ready to take the plunge and want to make beautiful background glows/rays to set off your Lone Star, just drop me a comment and I'll hold your hand through the process. Shoot, if you say please I'll likely do the math for you. Happy Sewing.
This also will work for reductions. Starting with an 8" paper pieced block and making it a 4". 4" divided by 8" equals .5 move the decimal twice to the left is a 50% reduction.
Note this is for paper pieced blocks as the only planned seam allowance is on the outside edge other traditionally pieced blocks are more complicated.