0.07847
g/g/day
8.8
days
200.0%
0.07847
g/g/day
8.8
days
200.0%
The Relative Growth Rate (RGR) Calculator computes the rate of mass increase per unit mass per unit time, the standard metric for comparing plant growth across species, treatments, or environmental conditions. RGR removes the influence of initial size, allowing meaningful comparisons between plants of different starting masses. It is one of the most fundamental parameters in plant growth analysis.
Enter the initial and final dry masses and the time interval to obtain RGR (in g/g/day), the doubling time, and the total percentage growth. This tool is essential for ecology experiments, crop growth studies, and plant physiology research.
The calculator uses the classical RGR formula:
RGR = (ln W₂ - ln W₁) / (t₂ - t₁)
Where W₁ and W₂ are the dry masses at times t₁ and t₂, and ln denotes the natural logarithm. This formula assumes exponential growth over the measurement interval. Additional outputs include:
RGR is typically expressed in g/g/day, meaning grams of new mass per gram of existing mass per day.
Inputs
Results
A seedling tripling its mass from 5 to 15 g in 14 days has an RGR of 0.078 g/g/day with a doubling time of 8.8 days.
Inputs
Results
A sapling growing from 100 to 120 g in 60 days has a much lower RGR of 0.003 g/g/day.
Absolute growth rate (grams per day) depends on plant size; a large plant naturally gains more mass per day than a small one. RGR normalizes for initial size, expressing growth as a rate per unit mass. This allows fair comparisons between species of different sizes, between developmental stages, or between experimental treatments. It is the plant equivalent of specific growth rate in microbiology.
Typical RGR values range from about 0.01-0.05 g/g/day for slow-growing woody species to 0.1-0.3 g/g/day for fast-growing herbaceous plants and seedlings. Aquatic plants and algae can have even higher RGR values. RGR generally decreases as plants get larger and older, as more biomass is allocated to structural support rather than new growth.
Yes. RGR is typically highest during early growth when most biomass is photosynthetic leaf tissue, and it declines as plants mature and allocate more resources to stems, roots, and reproductive structures. For this reason, RGR comparisons are most meaningful when made over the same growth stage or size range, and over short enough intervals that the assumption of exponential growth is reasonable.
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