How Many Slabs needed? Fitting Series of smaller rectangles (various L x W dimensions) into a larger rectangle (fixed L x W dimensions)

May be wrong, but I think this is just a 2D version of the Bin Packing Problem..
A countertop maker needs to figure out how many slabs of a certain size to order for a job. Each client's kitchen is a different layout, but the amount of material needed can be broken down into a series of small rectangles.

User should be able to change the dimensions of the master slab
User should be able to enter Length x Width dimensions for an unlimited series of rectangular pieces
Output should show # of slabs required & which pieces fit into each slab (see example below)

USER DEFINES
Slab = 120" x 56"
R1 = 4" x 72"
R2 = 4" x 30"
R3 = 26" x 60"
R4 = 36" x 58"
...etc

OUTPUT
_ = # of slabs required
... slab #1 contains pieces: ____
... slab #2 contains pieces: __
...etc.