Between 1/2 inch to 3/4 inch shrinkage.

Looks like you're really into math, Abigail, and good on you for that.

With nominal sizing, most dimensional lumber is around 1/2" smaller, when ready to use,

so maybe 3 1/2" by 7 1/2", length a bit less, too.

Real wood is not ready to use until seasoned, dried, and milled. Long story.