I trace the inner triangle of your frame to get an exact silhouette. I then decide on the width based on your bottom bracket. I use waterproof zippers, 1000 denier nylon, and nylon thread to build a bag worthy of hanging on your 3000$ bicycle (the yellow and green 9zero7 is mine). I also build rack bags using specific dimensions. All my bags are guaranteed for life; my life.
I welcome riders to trace off their own silhouette and mail it to me. I can build a perfect bag without ever seeing your cycle.