Featured contributor PhD Applied Physics; former research associate at a national metrology lab.

Dr. Helena Ortiz

Senior Reviewer, Science & Engineering

0 calculators 0 articles Member since Jun 2026

About the author

Helena is the senior technical reviewer for physics, chemistry, and unit-conversion calculators. She is the last pair of eyes on every formula — checking constants, units, and edge cases against primary sources and standards bodies.

She holds a PhD in Applied Physics and previously held a research post at a national metrology lab.

Areas of expertise

Physics Chemistry Unit conversion Measurement standards

Education & credentials

BSc Physics — Universidad Complutense de Madrid
PhD Applied Physics — Stanford University

Statistics

Two-Sample Independent t-Test Calculator

Calculates Welch's t-statistic and approximate degrees of freedom for comparing means of two independent samples.

Basic

17,895 4.2 1 min

Physics

Refractive Index from Speed of Light Calculator

Calculates the refractive index of a medium from the speed of light in that medium. Also computes the critical angle for...

Basic

23,011 4.8 1 min

Chemistry

Moles of Gas Collected Over Water from Total Pressure and Volume Calculator

Compute the moles of dry gas collected by water displacement: subtract the water-vapour partial pressure at the experime...

Basic

22,251 5.0 1 min

Chemistry

Mass Fraction to Empirical Formula Calculator

Converts mass percentages of C, H, O, and N into moles then divides by the smallest to get the empirical formula subscri...

Basic

11,573 4.0 1 min

Physics

Mean Free Path of an Ideal-Gas Molecule Calculator

Compute the mean free path λ — the average distance an ideal-gas molecule travels between collisions — from temperature,...

Basic

12,443 4.8 1 min

Physics

Relativistic Doppler Shift Calculator

Compute the relativistic (radial) Doppler shift of light from a source moving with β = v/c relative to the observer: f_o...

Basic

1,736 4.6 1 min

Chemistry

pH of Strong Acid + Strong Base Mixture Calculator

Compute the pH after mixing a volume of strong monoprotic acid with a volume of strong monoprotic base, by net moles and...

Basic

15,465 4.8 1 min

Chemistry

Gibbs Free Energy from Cell Potential Calculator

Compute the standard Gibbs free-energy change of an electrochemical reaction from its standard cell potential and the nu...

Basic

22,137 5.0 1 min

Chemistry

Percent Water of Hydration Calculator

Compute the percent water of hydration in a hydrated crystal from the mass of the hydrate before and after heating off t...

Basic

10,322 3.8 1 min

Physics / Mechanics

Gear Ratio Calculator

Compute the gear ratio, output rotational speed, and output torque of a single-stage spur-gear pair from the number of t...

Basic

19,258 4.6 1 min

Chemistry / Solutions

Titration Equivalence Point Volume Calculator

Calculates the volume of titrant solution required to completely neutralise a given analyte using n₁V₁ = n₂V₂. Applicabl...

Basic

6,581 4.8 1 min

Physics / Mechanics

Apparent Weight in an Accelerating Elevator Calculator

Compute the apparent weight (the normal force read by a bathroom scale) of a person in an elevator that is accelerating:...

Basic

8,083 4.3 1 min

Showing 145 to 156 of 540 results

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Reviewed by Dr. Helena Ortiz

These calculators were technically reviewed by Dr. Helena Ortiz for accuracy.

Health / Body Metrics

Cockcroft-Gault Creatinine Clearance Calculator

Estimate creatinine clearance (a proxy for kidney function used in drug dosing) using the Cockcroft-Gault equation.

Basic

16,409 4.0 1 min

Chemistry / Solutions

Gas Density Calculator

Compute the density of an ideal gas at given pressure and temperature from its molar mass, using ρ = PM/(RT).

Basic

4,981 4.2 1 min

Physics / Electricity

Current Divider Calculator

Compute the current through one branch of a two-resistor parallel current divider from the total source current.

Basic

13,508 4.7 1 min

Biology / Microbiology

Population Doubling Time Calculator

Compute how long a population (or culture, or investment) takes to double at a constant exponential growth rate using th...

Basic

19,562 3.9 1 min

Physics / Mechanics

Velocity Calculator

Compute velocity from displacement and time, or solve for either one given the other two.

Basic

20,035 4.1 1 min

Health / Body Metrics

Steroid Dose Equivalence Calculator

Convert a dose of one corticosteroid into the equivalent dose of another, using standard glucocorticoid potency multipli...

Basic

14,581 4.2 1 min

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Dr. Helena Ortiz

Two-Sample Independent t-Test Calculator

Refractive Index from Speed of Light Calculator

Moles of Gas Collected Over Water from Total Pressure and Volume Calculator

Mass Fraction to Empirical Formula Calculator

Mean Free Path of an Ideal-Gas Molecule Calculator

Relativistic Doppler Shift Calculator

pH of Strong Acid + Strong Base Mixture Calculator

Gibbs Free Energy from Cell Potential Calculator

Percent Water of Hydration Calculator

Gear Ratio Calculator

Titration Equivalence Point Volume Calculator

Apparent Weight in an Accelerating Elevator Calculator

Reviewed by Dr. Helena Ortiz

Cockcroft-Gault Creatinine Clearance Calculator

Gas Density Calculator

Current Divider Calculator

Population Doubling Time Calculator

Velocity Calculator

Steroid Dose Equivalence Calculator