Search conversion rate is the share of unique search sessions that ended in a purchase. It compresses the entire funnel — query understanding, ranking, product detail page, checkout — into one number. A typical ecommerce store sits around 2–4%; the search-traffic slice tends to convert 1.5–3× higher than browse traffic because shoppers have declared intent.
When you ship a search change, conversion rate is the metric that matters and the one that takes longest to read out (you usually need 1–2 weeks of A/B traffic for stat-sig). Faster proxies — CTR, NDCG, add-to-cart-from-search — let you iterate during development; conversion rate is the verdict.
Beware Simpson’s paradox: a search change can lift conversion in every individual category but lower aggregate conversion if it shifts traffic toward lower-converting categories. Always segment by query type or category before declaring a win.