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

Everyday Life / Shopping

Unit Price Best Deal Comparison Calculator

Compares unit prices of two products (price / quantity) to identify the better deal and shows percentage savings.

Basic

541 4.7 1 min

Physics

Half-Value Layer from Linear Attenuation Coefficient Calculator

Compute the half-value layer (HVL) — the thickness of a shielding material that reduces a monoenergetic beam of x-rays o...

Basic

6,836 4.6 1 min

Physics / Electricity

Parallel-Plate Capacitance Calculator

Compute the capacitance of a parallel-plate capacitor from the plate area A, the separation d, and the dielectric consta...

Basic

14,485 4.6 1 min

Statistics

Log-Normal Distribution μ & σ Calculator

Calculates the PDF, CDF, mean, median, mode, and variance of a log-normal distribution from its log-scale parameters μ a...

Basic

15,037 4.0 1 min

Chemistry

Gibbs-Helmholtz Free Energy Calculator

Calculates Gibbs free energy change ΔG from enthalpy ΔH, temperature T, and entropy change ΔS, indicating reaction spont...

Basic

8,101 4.2 1 min

Chemistry

Combustion Heat from Hess's Law Summation Calculator

Applies Hess's law to calculate the standard enthalpy of combustion: ΔH°_rxn = Σ(ν·ΔHf°)_products − Σ(ν·ΔHf°)_reactants...

Basic

24,943 3.9 1 min

Chemistry / Solutions

Buffer pH After Adding Strong Acid (Henderson–Hasselbalch) Calculator

Calculates the pH of a buffer after a known amount of strong acid is added, using the Henderson–Hasselbalch equation: pH...

Basic

23,741 4.1 1 min

Chemistry

First-Order Rate Constant from Half-Life Calculator

Compute the first-order rate constant k of a reaction (or radioactive decay) from its half-life t½: k = ln 2 / t½. Repor...

Basic

22,947 4.3 1 min

Physics / Mechanics

Telescope Magnification Calculator

Compute the magnification of a telescope from the focal lengths of the objective lens (or mirror) and the eyepiece, plus...

Basic

13,776 4.4 1 min

Chemistry

pH after Mixing Two Strong-Acid Solutions Calculator

Compute the resultant pH after mixing two strong-acid solutions of arbitrary molarity and volume. Strong acids fully dis...

Basic

6,127 4.9 1 min

Chemistry / Reactions

Acid-Base Titration Calculator

Compute the unknown concentration of a strong-acid / strong-base titration from the known concentration, the volume of t...

Basic

12,587 4.4 1 min

Physics / Mechanics

Elastic Collision Final Velocities Calculator

Calculates final velocities after a one-dimensional perfectly elastic collision between two objects using conservation o...

Basic

13,969 4.8 1 min

Showing 85 to 96 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

Unit Price Best Deal Comparison Calculator

Half-Value Layer from Linear Attenuation Coefficient Calculator

Parallel-Plate Capacitance Calculator

Log-Normal Distribution μ & σ Calculator

Gibbs-Helmholtz Free Energy Calculator

Combustion Heat from Hess's Law Summation Calculator

Buffer pH After Adding Strong Acid (Henderson–Hasselbalch) Calculator

First-Order Rate Constant from Half-Life Calculator

Telescope Magnification Calculator

pH after Mixing Two Strong-Acid Solutions Calculator

Acid-Base Titration Calculator

Elastic Collision Final Velocities 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