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

Half-Cell EMF from Standard Reduction Potentials (Nernst) Calculator

Calculates the standard cell potential E°_cell = E°_cathode − E°_anode and corrects for concentration using the Nernst e...

basic

14,679 4.5 1 min

Chemistry

Nuclear Binding Energy & Mass Defect Calculator

Calculates nuclear mass defect and binding energy (total and per nucleon) from proton/neutron counts and actual nuclear...

basic

2,553 4.4 1 min

Math

Cramer's Rule 2×2 Linear System Calculator

Solves a system of two linear equations ax+by=e, cx+dy=f using Cramer's Rule. Computes the main determinant D and soluti...

basic

20,650 4.2 1 min

Health

Simplified Disease Activity Index (SDAI) Calculator

Calculates the SDAI = TJC + SJC + Patient global (VAS) + Physician global (VAS) + CRP (mg/dL). Remission ≤ 3.3; low ≤ 11...

basic

2,872 4.6 1 min

Chemistry

pH of a Salt of a Weak Acid by Hydrolysis Calculator

Compute the pH of an aqueous solution of the conjugate base of a weak acid (A⁻ from a strong-base / weak-acid salt). The...

basic

10,007 4.8 1 min

Everyday Life

Gravel Volume (Cubic Yards) from Area and Depth Calculator

Calculates the volume of gravel required to cover a rectangular area to a specified depth: volume (yd³) = (length × widt...

basic

1,287 4.3 1 min

Physics

Photon Momentum from Wavelength Calculator

Compute the linear momentum of a photon directly from its wavelength using p = h / λ, with Planck's constant h = 6.62607...

basic

2,594 4.2 1 min

Chemistry

Bond Order from MO Theory Calculator

Compute the molecular-orbital bond order from the number of electrons in bonding and antibonding orbitals: BO = (n_bondi...

basic

21,783 4.1 1 min

Physics / Mechanics

Rolling Resistance Force from Load and Coefficient Calculator

Computes rolling resistance force F_r = C_rr · N, where C_rr is the dimensionless rolling resistance coefficient and N i...

basic

23,746 4.6 1 min

Chemistry

Enthalpy of Formation from Combustion Data Calculator

Compute a fuel's standard enthalpy of formation from its measured heat of combustion and the tabulated standard enthalpi...

basic

3,513 4.9 1 min

Physics / Mechanics

Angular Momentum Calculator

Compute the angular momentum of a rigid body using L = I · ω, plus the angular-momentum equivalent for a point mass movi...

basic

13,694 4.2 1 min

Sports

Basketball Player Efficiency Rating (PER) Calculator

Estimates a player's Player Efficiency Rating (PER) using a simplified box-score formula from points, rebounds, assists,...

basic

9,008 4.6 1 min

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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

Half-Cell EMF from Standard Reduction Potentials (Nernst) Calculator

Nuclear Binding Energy & Mass Defect Calculator

Cramer's Rule 2×2 Linear System Calculator

Simplified Disease Activity Index (SDAI) Calculator

pH of a Salt of a Weak Acid by Hydrolysis Calculator

Gravel Volume (Cubic Yards) from Area and Depth Calculator

Photon Momentum from Wavelength Calculator

Bond Order from MO Theory Calculator

Rolling Resistance Force from Load and Coefficient Calculator

Enthalpy of Formation from Combustion Data Calculator

Angular Momentum Calculator

Basketball Player Efficiency Rating (PER) Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator