Blanket overhead rate is single rate for:

1. Blanket rate is computed once for the entire factory using total overhead divided by total activity. 2. It ignores variation across departments. 3. Departmental rates are more accurate when departments differ materially in overhead intensity. 4. Hence blanket overhead rate applies to the whole factory. _Source: ICAI BoS Inter Paper 3, Ch 4 "Overheads", §4.5.3 ¶1_