A data processing system 2 supporting vector processing operations uses scaling vector length querying instructions. The scaling vector length querying instructions return a result which is dependent upon a number of elements in a vector for a variable vector element size specified by the instruction and multiplied by a scaling value specified by the instruction. The scaling vector length querying instructions may be in the form of count instructions, increment instructions or decrement instructions. The instructions may include a pattern constraint applying a constraint, such as modulo(M) or power of 2 to the partial result value representing the number of vector elements provided for the register element size specified for the instruction.