function calculatePlantGrowth() {
var initialSize = parseFloat(document.getElementById('initialSize').value);
var finalSize = parseFloat(document.getElementById('finalSize').value);
var timePeriod = parseFloat(document.getElementById('timePeriod').value);
var timeUnit = document.getElementById('timeUnit').value;
var resultsDiv = document.getElementById('results');
// Validation
if (isNaN(initialSize) || isNaN(finalSize) || isNaN(timePeriod)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (timePeriod <= 0) {
alert("Time elapsed must be greater than zero.");
return;
}
if (initialSize 0) {
doublingTime = Math.log(2) / rgrRaw;
doublingText = doublingTime.toFixed(2) + " " + timeUnit;
} else if (rgrRaw === 0) {
doublingText = "No growth";
} else {
doublingText = "Shrinking";
}
// Display Logic
resultsDiv.style.display = 'block';
// Formatting AGR
document.getElementById('agrResult').innerText = agr.toFixed(4);
var unitSuffix = "units"; // generic since user could enter cm or g
document.getElementById('agrUnit').innerText = unitSuffix + " per " + timeUnit.slice(0, -1); // remove 's' from unit
// Formatting RGR
document.getElementById('rgrResult').innerText = rgrPercent.toFixed(2) + "%";
document.getElementById('rgrUnit').innerText = "growth per " + timeUnit.slice(0, -1);
// Formatting Doubling Time
document.getElementById('doublingTimeResult').innerText = doublingText;
}
How to Calculate Plant Growth Rate
Measuring plant growth is essential for agriculture, botany, and home gardening. It helps determine the health of a crop, the efficacy of fertilizers, and the ideal harvest time. There are two primary ways to quantify growth: Absolute Growth Rate (AGR) and Relative Growth Rate (RGR).
1. Absolute Growth Rate (AGR)
AGR measures the simple arithmetic increase in size over a specific time period. It tells you exactly how much height, weight, or leaf area has been added per day or week.
AGR = (W₂ – W₁) / (t₂ – t₁)
W₁: Initial size (height, biomass, etc.)
W₂: Final size
t₂ – t₁: The time interval between measurements
Example: If a corn stalk is 10cm tall on Day 1 and 15cm tall on Day 6, the AGR is (15 – 10) / 5 = 1 cm/day.
2. Relative Growth Rate (RGR)
RGR is often considered a more accurate measure of biological efficiency because it accounts for the initial size of the plant. A small seedling gaining 1 gram is growing much faster "relatively" than a large tree gaining 1 gram. RGR assumes growth is exponential (compound interest logic applied to biology).
RGR = (ln(W₂) – ln(W₁)) / (t₂ – t₁)
ln: Natural logarithm
Result: Often expressed as a percentage or g/g/day
This formula flattens the curve of exponential growth to a linear value representing efficiency.
Why Measure Plant Growth?
Understanding the rate at which your plants develop allows you to:
Optimize Fertilization: If growth slows (low AGR/RGR) during a vegetative phase, nutrient deficiency might be the cause.
Predict Harvests: Using the doubling time metric, farmers can estimate when crops will reach marketable size.
Compare Varieties: Calculate RGR to see which genetic strain performs better under identical environmental conditions.
Common Metrics for Size (W)
Metric
Unit
Best For
Height
cm, meters
Stem crops (corn, sunflower), trees.
Biomass (Dry Weight)
grams, kg
Scientific accuracy. Requires drying the plant (destructive).
Leaf Area
cm²
Photosynthetic efficiency studies.
Node Count
number
Vegetative tracking in vining plants.
Factors Affecting Growth Rate
If your calculator results are lower than expected, consider these limiting factors: