Cell Passage Split Ratio Calculator
Plan a passage: from current confluence, doubling time and when you next need the cells, find the split ratio, cells per flask and expected confluence at pickup.
How it works
Split ratio = current % × 2^(hours ÷ doubling time) ÷ target %
Cells grow exponentially, so the right split depends on how many doublings fit before you return: 72 hours at a 24-hour doubling time is 8× growth, so 90% confluent cells need roughly a 1:9 split to reach 80%. Standard ratios (1:3 to 1:10) are fine; going beyond 1:20 risks slow recovery in many lines.
Worked example
90% confluent, 24 h doubling, needed in 72 h at 80%: 90 × 8 ÷ 80 = 9 → round up to a 1:10 split (about 72% when you return).
Frequently asked questions
How do I find my doubling time?
Count cells at two time points in log phase: DT = t × ln2 ÷ ln(N₂/N₁). The cell doubling time calculator does this.
Why record population doublings?
Passage number depends on split ratios; cumulative doublings track true cell age for senescence and phenotype drift.
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For teaching and planning — verify against your lab protocol and instrument documentation.