The most accurate estimate is done with an onsite visit.  Many variables (that you might not consider) can impact the overall time it takes to move; disassembly and reassembly, protecting glass or fragile items for safe transport, how close the truck can park to the items,  availability of an elevator, number of stairs to carry,  amount and size of the furniture and the total number of boxes.   An accurate inventory list of furniture, equipment and boxes is essential to avoiding "surprises" and extra costs at the time of billing.