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
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
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
Calculate student loan repayment with an optional grace period and subsidized/unsubsidized interest. Unsubsidized loans accrue interest during the grace period that capitalizes into principal; subsidized loans do not. Shows monthly payment, total interest, total repayment, a balance curve, and a yearly breakdown.
student-loan-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
Practice significant-figure rules with step-by-step feedback: count sig figs, round to N sig figs, convert to scientific notation, and propagate through +/−/×/÷.
significant-figures-sandboxMath & Numbers
Convert US tablespoons to US teaspoons with configurable decimal precision
tablespoon-to-teaspoonMath & Numbers
Convert square meters to hectares with configurable decimal precision
square-meter-to-hectareMath & Numbers
Convert square centimeters to square inches with configurable decimal precision
square-cm-to-square-inchMath & Numbers
Convert square inches to square centimeters with configurable decimal precision
square-inch-to-square-cm