Audience size by lookback window and site traffic level.
Inputs
Post-iOS14: 50-70% typical
Pool sizes
Pool
Estimated size
Status
About this calculator
Retargeting pool size determines whether retargeting can spend efficiently. Below 1,000 active users in your lookback window, ad sets struggle to deliver. Below 5,000, retargeting spends but cannot scale. Above 10,000 unlocks meaningful retargeting volume across multiple offers and lookback tiers.
This calculator estimates pool sizes by traffic level, match rate (post-iOS14 you only see 50-70% of visitors), and lookback window. The math: monthly visitors × match rate × (window/30) = pool size for that window. Then break down by funnel stage (all visitors, ATC, purchasers) to size each retargeting audience.
The strategic implication: retargeting can\'t fix an undersized prospecting program. If your top-of-funnel traffic is small, retargeting is small, and the only path to growing retargeting is growing acquisition. Trying to over-spend on a thin retargeting pool produces high CPMs and ad fatigue fast.
Pair with the Tracking Gap Estimator (sizes the pixel match-rate problem) and the Audience Overlap Estimator (avoid bidding against yourself). Modern Advantage+ campaigns can absorb retargeting into broader audiences if pools are too small for standalone targeting.
Frequently asked questions
What's the right lookback window?
30-day window for most ecommerce. 7-day for short-cycle products. 90-180 day for long-cycle considered purchases. Longer windows = larger pool but lower intent. Sweet spot is 30 days for most DTC.
When is retargeting pool too small?
Below 1,000 active users in 30 days, retargeting can't spend efficiently. Below 5,000, it spends but won't scale. Above 10,000 active users provides meaningful retargeting volume.
How do I grow the retargeting pool?
Drive more top-of-funnel traffic. Retargeting pool size is a downstream metric of upstream acquisition. Brands trying to "scale retargeting" without growing prospecting are stuck.
Should I retarget add-to-cart vs purchase?
Both, separately. ATC abandoners convert at 3-5% with retargeting (high intent, recent activity). Past purchasers convert at 8-15% with cross-sell/upsell offers. Combine into one ad set only if either pool is too small alone.
What about iOS14 retargeting limitations?
Pixel-based retargeting (browsers) lost 30-50% of iOS users. Customer list retargeting (uploaded emails) still works. CAPI server-side retargeting recovers most of the iOS gap. Use multiple methods stacked.