Math & Numbers
Calculate the critical (resonance) speed of a rotating shaft using the single-DOF rotor model. ω_n = √(k/m), n_cr = (60/2π)·√(k/m) rpm. Also returns the natural frequency f_n in Hz.
shaft-critical-speedMath & Numbers
Convert between bolt tightening torque and axial clamp force. T = K·F·d, where K is the nut factor (~0.20 for dry steel). Solve torque from force, or force from torque.
bolt-torque-clamp-forceMath & Numbers
Calculate the power transmitted by a rotating shaft. P = T·ω = 2π·n·T/60. Solve power from torque and speed, or torque from power and speed. Supports W/kW/hp.
shaft-power-calculatorMath & Numbers
Calculate the elastic potential energy and force of a spring in compression or extension. U = ½·k·x², F = k·x. Solve energy from displacement, or displacement from energy.
spring-compression-energyMath & Numbers
Calculate the stiffness (spring rate) of a cylindrical helical compression/extension spring. k = G·d⁴ / (8·D³·n) in N/mm. Includes shear-modulus presets for common spring materials.
spring-rate-calculatorFinance
Calculate the true Annual Percentage Rate (APR) of a loan when upfront fees are involved. The nominal interest rate sets the monthly payment, but fees reduce the net cash received, raising the effective APR. Uses Newton's method to solve the annuity present-value equation. Shows APR, nominal rate, monthly payment, and the APR premium.
apr-calculatorFinance
Compare avalanche (highest APR first) vs snowball (lowest balance first) strategies for paying off multiple credit cards. Enter cards as 'name, balance, APR%, minPayment%' per line plus an extra monthly payment. Shows payoff time, total interest, savings vs minimum-only, and balance decline curves.
credit-card-payoffFinance
Convert between hourly, monthly, and annual salary. Enter any one figure and get the other two, with customizable hours per week, weeks per year, and overtime multiplier. Shows paycheck estimates for weekly, biweekly, semimonthly, and monthly pay periods.
salary-converterFinance
Two-phase retirement model: an accumulation phase (current age to retirement, with monthly contributions and compound growth) and a withdrawal phase (retirement to life expectancy, nest egg grows at a conservative rate while inflation-adjusted withdrawals are taken out). Reports whether the nest egg lasts, real purchasing power, and any shortfall.
retirement-calculatorFinance
Solve for the monthly contribution needed to reach a savings goal (with interest and compounding), or for the time required to reach the goal with a fixed monthly deposit. Optional inflation adjustment. Uses monthly compounding rollup.
savings-calculatorMath & Numbers
Exponential decay for radioactive isotopes and drugs: remaining amount, derived half-life, time to target, or steady-state accumulation. Uses N(t) = N0·e^(-λt).
half-life-calculatorMath & Numbers
Compute buoyant force, fluid density, or displaced volume from any two, with optional float/sink analysis
buoyancy-calculator