Calculate ET50, time T, or percent floating at time T from any two values using a linear leaf disk flotation estimate with steps shown.
ET50 Formula
The ET50 calculator uses a linear estimate that assumes 0% of the leaf disks are floating at time 0. If you enter any two values, it solves for the missing value.
- ET50 = estimated time for 50% of the leaf disks to float, in minutes
- T = the time at which you measured the floating leaf disks, in minutes
- PFL = percent of leaf disks floating at time T, as a percentage from 0 to 100
If you enter T and PFL, the calculator estimates ET50. If you enter ET50 and PFL, it calculates the time needed to reach that percent floating. If you enter T and ET50, it estimates the percent of disks that should be floating at that time under the same linear assumption.
ET50 Result Interpretation
In comparable leaf-disk trials, lower observed ET50 means faster 50% flotation and is an indirect measure of net photosynthetic response. A single-point linear estimate need not equal the observed crossing. The qualitative table has no universal numerical thresholds.
| ET50 result | General meaning | Common interpretation |
|---|---|---|
| Low ET50 | 50% flotation was reached quickly | Faster net flotation response in comparable trials |
| Moderate ET50 | Between the comparison trials; no universal average | Useful for comparing against other trials or treatments |
| High ET50 | 50% flotation took longer | Slower net flotation response in comparable trials |
Percent Floating Quick Reference
| Number of disks floating | Total disks | PFL |
|---|---|---|
| 2 | 10 | 20% |
| 4 | 10 | 40% |
| 5 | 10 | 50% |
| 7 | 10 | 70% |
| 9 | 10 | 90% |
Examples
Example 1: Calculate ET50
You record that 40% of the leaf disks are floating after 8 minutes.
The estimated ET50 is 10 minutes.
Example 2: Calculate percent floating
You know the ET50 is 12 minutes and want to estimate the percent floating at 9 minutes.
The estimated percent floating at 9 minutes is 37.5%.
FAQ
What does ET50 mean?
ET50 means the estimated time needed for 50% of the leaf disks to float. In a leaf disk photosynthesis assay, disks float as oxygen accumulates from photosynthesis. ET50 is often used to compare how quickly disks respond under different light levels, bicarbonate concentrations, temperatures, or other treatments.
Why is this only an estimate?
This calculation assumes the percent floating increases in a straight line from 0% at time 0. Real data may not be perfectly linear. For a more accurate ET50, use several time points and identify where the data crosses 50%, or interpolate between the two measured points closest to 50%.
Can PFL be 0 when calculating ET50?
No. If PFL is 0, the formula would require division by zero. You need a nonzero percent floating value to estimate ET50 from a single time point.
