log2FC ↔ Fold Change Online Converter

Differential expression results are reported as log2FC, but when describing results, researchers typically say “upregulated X-fold.” The relationship between the two is:

FC = 2 ^ log2FC          log2FC = log2(FC)

Why log2? Raw fold changes are asymmetric: a 2-fold upregulation is 2, but a 2-fold downregulation is 0.5. All downregulated genes are crammed between 0 and 1, while upregulated genes spread from 1 to infinity — awkward for both plotting and statistics. After log2 transformation, a 2-fold upregulation becomes +1 and a 2-fold downregulation becomes −1, symmetric around 0.

Common threshold reference:

Important note: The log2FC threshold and statistical significance (p / q value) are two independent filters that must be applied together. Filtering on fold change alone without a q-value cutoff lets random noise in lowly expressed genes masquerade as large fold changes; filtering on q value alone without a fold-change cutoff flags tiny changes in highly expressed genes that are statistically significant but biologically meaningless.