Load size is a machine question as well as a clothing question
A washer needs enough space for its designed wash action. Capacity and loading instructions vary by model, so the appliance manual is the best source for the machine-specific limit.
Do not pack the drum tightly
Overloading can reduce movement, rinsing and cleaning performance. The American Cleaning Institute also identifies overloading as a contributor to laundry problems such as lint deposition.
Full loads can improve efficiency
ENERGY STAR recommends running full loads when practical because clothes washers use substantial resources per cycle. “Full” should still mean a load that fits the machine’s loading guidance, not a tightly compressed drum.
Keep unlike care needs separate
Do not create a larger load by mixing items whose care instructions, soil level or lint behavior conflict. A correctly sized load still needs compatible washing conditions.
Garment care labels, appliance manuals and laundry-product directions can be more specific than a general guide. Use them when they set a tighter limit.