While this question may seem like it should be fairly straight forward, the answer is that there is no magic formula to predict the amount of money that a pedestrian accident case may be worth.
Generally, an injured pedestrian is entitled to compensation to pay for all medical treatment (both past and future treatment that is reasonably expected) caused by the accident, loss of past wages, loss of future wage earning capacity, and general damages (typically referred to as "pain and suffering" damages).
The largest factor in determining the value of a pedestrian injury accident case is the total amount of medical bills, extent of the injuries themselves, and length of time it took to recover. Whether the pedestrian has been left with a permanent injury or not is another big factor. Not only are the medical bills subject to reimbursement through a settlement or judgment, but they are the primary measure used by insurance companies and jurors to award general damages.
To really determine what your Washington pedestrian case is worth it's best to talk to an experienced, knowledgeable attorney who will fight to get the settlement you deserve.