The quality of capacity planning significantly affects firm profitabil
ity, particularly for firms in service industries. In practice, firms
use product cost data to infer the expected cost of under-and over-sto
cking capacity and to determine installed capacity. Theory shows that
this is not optimal practice. In light of the informational and comput
ational complexities associated with the optimal theoretical formulati
on, the use of product cost may be justified as a heuristic. For a mul
ti-product, multi-resource firm, we use simulations to investigate the
efficiency of four cost-based decision rules in determining the expec
ted cost of under-and over-stocking capacity. Results indicate surpris
ingly high performance levels, relative to a benchmark solution, The p
erformance of the product-based planning rule deteriorates as products
increasingly share capacity resources, The opposite is true for resou
rce-focused rules. There appears to be significant value from identify
ing mechanisms to balance installed capacity across resources.