A great tool when trying to estimate wheat yield:
Estimating Wheat Yield

A great resource for growth staging wheat with pictures
Growth Stages of Wheat

Helpful equations to estimate wheat yield in Western Kansas:
Yield estimated before heading (bu) =((stems per foot x 0.531 + 8.5)x 0.531 / row spacing (inches)) x 19.213

Yield estimated after heading (bu) = (heads per foot x 0.513) / row spacing (inches)) x 19.213

Adjustments to yield:
Replace the coefficient 0.513 with 0.409 for a poor year or 0.618 for a good year.