chrome://calculator/content/calculator.xul
This free calculator does conversions if you really need them. I'm metric but quilt in imperial but mostly sew(garments) using metric patterns.
For your 1/4 seam allowance there's no need to convert as your 1/4" is (approximately) 0,6 which is used in metric. I use conversions only when I'm not sure how much fabric to buy or to visualize the size of a project. Otherwise I 'm fine with inches. By the way, when you think metric (1m for 1yd) you never run short as 1 meter equals to 39,37 inches! I' attaching a table of conversions, just in case. Have fun!