Differential Expression · Fold Change · log2FC
Log2 Fold Change Calculator
The log2 fold change calculator converts linear fold change (FC) to log2 fold change (log2FC) and back, or calculates the expression ratio, signed fold change, and percent change directly from treatment and control measurements.
Interactive Fold Change & log2FC Converter
Formula: log₂FC = log₂(FC) = ln(FC) ÷ ln(2); Linear FC = 2^(log₂FC).
Formula: How to Calculate Fold Change & log2 Fold Change
In gene expression (RNA-seq, microarray, RT-qPCR) and proteomics workflows, fold change measures the ratio between a treatment condition and a baseline control. Transforming the linear ratio to base-2 logarithm centers unchanged expression at 0 and makes upregulation and downregulation symmetric:
Log2 Fold Change (log2FC) to Linear Fold Change Reference Table
Standard thresholds used in differential gene expression volcano plots and screening cutoffs (such as |log2FC| ≥ 0.585 for 1.5-fold change or |log2FC| ≥ 1.0 for 2-fold change):
| log2 Fold Change (log2FC) | Linear Ratio (Treatment / Control) | Signed Fold Change | Percent Change (%) |
|---|---|---|---|
| −3.3219 | 0.10× | −10.0× | −90.0% |
| −2.0000 | 0.25× | −4.0× | −75.0% |
| −1.0000 | 0.50× | −2.0× | −50.0% |
| −0.5850 | 0.67× | −1.5× | −33.3% |
| 0.0000 | 1.00× | 1.0× | 0.0% |
| +0.5850 | 1.50× | +1.5× | +50.0% |
| +1.0000 | 2.00× | +2.0× | +100.0% |
| +1.5000 | 2.83× | +2.83× | +182.8% |
| +2.0000 | 4.00× | +4.0× | +300.0% |
| +3.0000 | 8.00× | +8.0× | +700.0% |
| +3.3219 | 10.00× | +10.0× | +900.0% |
Interpreting Ratio Direction, Downregulation & Zero Counts
Symmetry of base-2 logarithmic scale
On a linear scale, a 2-fold increase is 2.0 while a 2-fold decrease is 0.5, compressing all downregulated genes between 0 and 1. On a log2 scale, doubling is +1.0 and halving is −1.0, giving equal visual weight on volcano and MA plots.
Contrast order (Treatment vs. Control)
Always verify whether a table defines the contrast as Treatment ÷ Control or Control ÷ Treatment. Reversing the numerator and denominator flips the sign of log2FC (+1.5 becomes −1.5) while inverting the linear ratio.
Handling zero values & pseudocounts
Because division by zero and log₂(0) are undefined, raw zero counts in sequencing or intensity assays require a domain-appropriate pseudocount (e.g., count + 0.5 or count + 1) or model-based shrinkage prior to log transformation.
Related Gene Expression & qPCR Calculators
Working with cycle threshold (Ct) values or standard curves? Use these companion quantitative PCR calculators:
Frequently Asked Questions
What does a log2 fold change of 1 or 1.5 mean?
A log2 fold change of +1.0 equals a 2-fold increase (+100% change, 2¹ = 2). A log2 fold change of +1.5 equals a 2.83-fold increase (+182.8% change, 2¹·⁵ ≈ 2.8284), while +0.585 corresponds to a 1.5-fold increase (+50% change).
How do you convert negative log2 fold change to fold change?
Raise 2 to the power of the negative log2FC value: FC = 2^(log2FC). For example, log2FC = −1 gives 2⁻¹ = 0.50 (half of the control level, or a 2-fold downregulation / −50% change), and log2FC = −2 gives 2⁻² = 0.25 (4-fold downregulation / −75% change).
Why is |log2FC| ≥ 1 or |log2FC| ≥ 0.585 commonly used as a cutoff?
A threshold of |log2FC| ≥ 1 selects genes with at least a 2-fold increase (FC ≥ 2.0) or 2-fold decrease (FC ≤ 0.5). A milder cutoff of |log2FC| ≥ 0.585 corresponds to at least a 1.5-fold change (FC ≥ 1.5 or FC ≤ 0.667).
How do I calculate log2 fold change in Excel or R?
In Excel, use =LOG(Treatment/Control, 2) or =LOG(FC, 2), and convert back with =2^log2FC. In R, use log2(treatment / control) and 2^log2fc.
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