If you’ve ever guessed your way through arrow spine charts or wondered why the “recommended” setup never quite shoots right off your recurve or longbow, you’re not alone. Many arrow spine charts and calculators are built around compound bows and elevated rests — they don’t account for how a longbow or selfbow actually flexes an arrow around the riser, or how much a Fast Flight string changes your real draw weight.

That’s why we designed the Arrow Builder tool below: a free arrow spine and FOC calculator made specifically for traditional archery. Our goal was to create a tool that is simple and intuitive to use, and that gives you advanced options if you want to go deeper. Every step explains the math so you can see and understand it clearly, and easily make adjustments for different bow and arrow setups. Check out the calculator tool out below. We also have articles that go deeper into arrow spine and FOC.