You can't beat a chronograph for accurately determing your bow speed. But you don't always have a chrono when you want, one at least I don't. However You can still make a reasonable estimation of your bow speed using only your bow, arrows, a target, a messureing tape and the table at the end of this document.

Here's how it works. Pick a target at a distance you can shoot good groups at, the farther the better, lets go with 30yrds away. Here are the steps.

Shoot a few arrows at a spot using your 30yrd pin.

Shoot a few more at the same spot using your 20 yrd pin, These shots will go low so make sure the lower shots won't hurt your arrows.

Meassure the seperation distance between the 30yrd group of arrows and the 20yrd group of arrows.

Heres the Chart.

DISTANCE= 90ft and 60ft (30yrds and 20yrds)

INCHES= 8 9 10 11 12 13 14 15 16 17 18 19
FPS=322 310 294 280 268 258 248 240 232 225 219 213

DISTANCE=60ft and 30ft (20yrds and10yrds)

INCHES= 5 6 7 8 9 10 11 12 13 14 15 16
FPS= 322 294 272 255 240 228 217 208 200 192 186 180

The 60ft and 30ft are calulated for lower for the slower bows, works good for the tradtional style bows.
I cant get everything to lineup but you get the idea 8 In is 322fps 9 is 310 and so on. I hope this will help.