What KPIs should you track for spare parts inventory management?

Five metrics cover most of what matters, and they only make sense read together.

Service level or fill rate, tracked per criticality class rather than as one site-wide figure, because a 95% average can hide 80% on your critical parts. Stockout frequency and duration, with duration the more telling of the two since it maps directly to equipment downtime. Inventory turnover, expected to be low on spare parts and best compared to a reference's own history rather than to a finished-goods benchmark. Inventory value tied up, split between critical and non-critical parts. And the obsolescence or slow-moving rate, the share of references with no movement over 12 or 24 months, which is where hidden losses accumulate.

The pairing that tells you whether the policy is working is service level against inventory value. Improving one at the expense of the other is not a result. Saint-Gobain Sekurit AGR moved both at once: service level from 95.8% to 97.2% while inventory fell 9%.