Free Online Calculators
From BMI to loans, tips to age — instant calculations at your fingertips.
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Rule of 70 Doubling Time Calculator
Estimates the number of years required for a value to double based on the annual growth rate using the Rule of 70.
Joule Heating Power Calculator (I²R)
Calculates the electrical power dissipated as heat in a resistor using the Joule heating formula I²R.
Loan Constant Calculator
Calculates the loan constant (mortgage constant), which is the ratio of annual debt service to total loan amount expressed as a percentage.
Simple Pendulum Period Calculator
Calculates the time period of a simple pendulum using its length and gravitational acceleration (small-angle approximation).
Child Waist-to-Height Ratio Calculator
Calculates the child waist-to-height ratio using waist circumference and height measurements.