Biology Calculators

Plug in your values below and get instant results for common biology formulas — no sign-up, no fuss.

Body Mass Index

BMI = mass / height²

Calculate BMI from body mass and height (used as a general screening measure).

Weight (kg)

Height (cm)

M = image size / actual size

Work out the magnification of a microscope image from image size and real (actual) size — use the same units for both.

Image size (mm)

Actual size (mm)

SA:V (cube) = 6ℓ² : ℓ³

Explore how surface area to volume ratio changes with size, modelled as a cube of side length ℓ.

Side length (mm)

N = N₀ e^rt

Estimate population size after time t, given a starting population and growth rate.

Starting population (N₀)

Growth rate per period (%)

Number of periods (t)

Max HR = 220 − age

Estimate maximum heart rate and a moderate-intensity training zone (50–85% of max) from age.

Age (years)

Mifflin–St Jeor equation

Estimate resting daily energy expenditure from weight, height, age, and sex.

Weight (kg)

Height (cm)

Age (years)

Sex

Results are for general educational reference only, not medical advice.