ET50 Calculator - Calculator Academy

Enter the percent of leaf disks floating (%) measured at a known time T (min) into the ET50 Calculator. This calculator returns an estimated ET50 assuming the percent floating increases linearly from 0% at time 0.

ET50 Formula

The example problem below outlines the steps and information needed to calculate an estimated ET50 from a single measurement. In many leaf-disk flotation assays, ET50 is more accurately obtained by interpolating between timepoints around 50% floating (or by curve fitting) rather than assuming linearity from time 0.

ET50 = T \times \frac{50}{PFL}

Variables:

ET50 is the estimated time at which 50% of leaf disks are floating (min)
PFL is the percent of leaf disks floating at time T (%)
T is the time at which PFL was measured (min)

To estimate ET50 from a single timepoint, multiply the measured time by 50 and divide by the measured percent floating.

How to Calculate ET50?

The following steps outline how to estimate ET50 using the linear method shown above.

Determine the percent of leaf disks floating at a chosen time T, PFL (%).
Determine the corresponding time, T (min).
Use the formula: ET50 = T × (50 / PFL).
Calculate ET50 (this result is an estimate assuming linear behavior from 0% at time 0).
After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem :

Use the following variables as an example problem to test your knowledge.

percent floating at time T, PFL (%) = 60

time, T (min) = 3

ET50 = T × (50 / PFL) = 3 × (50 / 60) = 2.5 min (estimated)

Follow-Up Calculations

If your setup is ET50 and you switch to ET30, each wheel moves 20 mm farther outboard, which adds roughly 98 N·m of extra bending moment to a 500 kg corner load. You can estimate wheel bearing load to see whether that offset change is likely to shorten hub and bearing life, especially on heavy SUVs or wide tires.

Changing from ET50 to ET30 widens track width by 40 mm total, so a car with a 1,600 mm front track gains about 2.5% more stance width. If you want to estimate cornering forces, that wider footprint can slightly reduce weight transfer and help the tires use lateral grip more effectively in the same turn.

An ET50 wheel swapped to ET20 places the tire 30 mm farther outboard, which increases leverage on bearings, ball joints, and sometimes fender liners, turning a fitment change into a potential repair expense over time. You can estimate long-term repair costs to compare the price of a safer wheel setup against the savings of keeping your current parts.