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

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

Chemistry / Solutions

Molality from Moles of Solute and Mass of Solvent Calculator

Calculates molality m = n_solute / mass_solvent (kg). Used in colligative property calculations where mass-based concent...

basic

17,553 3.9 1 min

Everyday Life

Date Difference in Days, Weeks, Months, and Years Calculator

Given the difference in days between two dates, converts to weeks, approximate months (÷30.44), and years (÷365.2425).

basic

24,071 4.5 1 min

Statistics / Probability

Expected Value of a Discrete Distribution Calculator

Calculates the expected value E[X] = Σ xᵢ·P(xᵢ) and variance Var[X] = Σ(xᵢ−μ)²·P(xᵢ) for a discrete probability distribu...

basic

24,910 4.2 1 min

Chemistry

Compressibility Factor Z from Real-Gas P, V, n, T Calculator

Compute the compressibility factor Z = PV / (nRT) for a real gas given pressure (atm), volume (L), moles, and temperatur...

basic

15,117 3.9 1 min

Chemistry

Gibbs Free Energy from Enthalpy and Entropy Calculator

Calculates the Gibbs free energy change ΔG and equilibrium constant K from enthalpy (ΔH in kJ/mol), entropy (ΔS in J/mol...

basic

21,658 4.7 1 min

Chemistry / Reactions

Nernst Equation Calculator

Compute the actual cell potential E from the standard potential E°, the number of electrons transferred n, and the react...

basic

23,565 4.7 1 min

Health

Child-Pugh Liver Cirrhosis Score Calculator

Calculates Child-Pugh score from bilirubin, albumin, INR, ascites, and encephalopathy to classify liver cirrhosis severi...

basic

7,061 4.6 1 min

Chemistry / Solutions

Stock Solution Preparation from Molarity Calculator

Calculates the volume of a concentrated stock solution needed to prepare a working solution of given molarity and volume...

basic

19,813 4.2 1 min

Physics

Photon Energy from Wavelength Calculator

Calculates photon energy from wavelength using E = hc/λ. Outputs energy in both electron-volts (eV) and joules (J). Ente...

basic

18,526 3.8 1 min

Chemistry

Acid-Base Titration Equivalence Point Calculator

Calculates the volume of titrant needed to reach the equivalence point in an acid-base titration from the concentrations...

basic

12,684 4.5 1 min

Chemistry

pH of a Strong Base from Molarity Calculator

Compute the pH of a strong base solution from its analytical concentration. With complete dissociation [OH⁻] = C, pOH =...

basic

7,754 5.0 1 min

Physics

Photoelectric Effect Maximum Kinetic Energy Calculator

Compute the maximum kinetic energy of a photoelectron emitted by an incident photon of frequency f striking a metal of w...

basic

8,687 4.5 1 min

Showing 157 to 168 of 504 results

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Reviewed by Dr. Helena Ortiz

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

Chemistry / Reactions

Equilibrium Constant Calculator

Compute the equilibrium constant K_c from the concentrations of two products (with stoichiometric coefficients 1) divide...

basic

5,060 4.0 1 min

Conversions / Length

Length Converter

Convert between meters, kilometers, miles, feet, inches, and yards.

Featured basic

4,964 4.2 1 min

Chemistry / Solutions

Combined Gas Law Calculator

Find the missing pressure, volume, or temperature using the combined gas law for a fixed amount of gas.

basic

5,360 4.2 1 min

Physics / Electricity

Capacitance Calculator

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

basic

12,524 4.1 1 min

Chemistry / Solutions

pOH Calculator

Compute pOH from hydroxide ion concentration and the matching pH at 25 °C.

basic

18,221 4.2 1 min

Ecology / Carbon Footprint

Carbon Footprint Calculator

Estimate your annual personal CO₂e footprint from home energy, driving, flying, and diet — with adjustable emission fact...

Featured basic

15,825 4.9 1 min

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Dr. Helena Ortiz

Molality from Moles of Solute and Mass of Solvent Calculator

Date Difference in Days, Weeks, Months, and Years Calculator

Expected Value of a Discrete Distribution Calculator

Compressibility Factor Z from Real-Gas P, V, n, T Calculator

Gibbs Free Energy from Enthalpy and Entropy Calculator

Nernst Equation Calculator

Child-Pugh Liver Cirrhosis Score Calculator

Stock Solution Preparation from Molarity Calculator

Photon Energy from Wavelength Calculator

Acid-Base Titration Equivalence Point Calculator

pH of a Strong Base from Molarity Calculator

Photoelectric Effect Maximum Kinetic Energy Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator