Learning Curve Calculator (Wright & Crawford Models)

How it works

b = log₂(learning rate) · Crawford (unit): Tₙ = T₁ × nᵇ · Wright (cumulative average): Average(n) = T₁ × nᵇ, Total(n) = n × Average(n), Tₙ = Total(n) − Total(n − 1)

The learning curve, first published by T. P. Wright in 1936 for aircraft production, says that every time cumulative output doubles, the labor time (or cost) falls to a fixed percentage of its previous value — the learning rate. In Wright’s original model that percentage applies to the cumulative average time; in the Crawford unit model, used by most US defense cost estimators, it applies to the time of each individual unit. Typical learning rates are 75–85% for complex assembly, around 90% for machining and 95% or more for highly automated work.

Worked example

With a first unit taking 100 hours and an 80% learning rate, b = log₂(0.8) = −0.3219. In the Crawford unit model unit 2 takes 80.00 hours, unit 4 takes 64.00 and unit 10 takes 100 × 10^−0.3219 = 47.65 hours. The first 10 units take 631.54 hours in total, an average of 63.15 hours each.

Sources: Experience curve effects — Wright’s learning curve · NASA Cost Estimating Handbook

Frequently asked questions