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

Physics / Mechanics

Newton's Gravitational Force Calculator

Compute the gravitational attraction between two point masses (or spherical bodies) at a centre-to-centre distance r, us...

basic

10,695 4.4 1 min

Finance

Markup and Gross Margin from Cost and Selling Price Calculator

Calculates markup % = (Price − Cost)/Cost × 100 and gross margin % = (Price − Cost)/Price × 100. Also shows required sel...

basic

23,354 4.1 1 min

Chemistry

Partition Coefficient (log P) from Concentration Ratio Calculator

Determines the partition coefficient P (and its logarithm log P) of a solute distributed between two immiscible solvents...

basic

1,004 4.7 1 min

Everyday Life

Solar Panel Array Area for a Daily-kWh Target Calculator

Compute the solar-panel array area needed to produce a target daily energy (kWh) at a site with average peak-sun-hours (...

basic

7,346 4.4 1 min

Everyday Life

Typing Speed Words Per Minute Calculator

Calculates typing speed (WPM), accuracy-adjusted net WPM, and characters per minute (CPM) from the number of words typed...

basic

297 4.9 1 min

Chemistry

Half-Life of a Zero-Order Reaction Calculator

Compute the half-life of a zero-order reaction A → products from the rate constant k (M·s⁻¹) and initial concentration [...

basic

13,129 4.8 1 min

Chemistry

Reaction Rate from Concentration Change Calculator

Compute the average reaction rate from the change in concentration of a reactant (or product) over a time interval: r =...

basic

4,525 3.9 1 min

Chemistry

Electronegativity Difference Calculator

Compute the difference in Pauling electronegativity between two atoms and classify the bond as nonpolar covalent (Δχ < 0...

basic

22,574 4.5 1 min

Chemistry

Arrhenius Rate Constant Calculator

Compute the rate constant k of a reaction at a given temperature from the Arrhenius pre-exponential factor A, the activa...

basic

23,388 4.9 1 min

Physics / Mechanics

Bernoulli Equation Calculator

Solve Bernoulli's equation for the static pressure at point 2 along a streamline given point-1 pressure, velocities at b...

basic

13,937 4.3 1 min

Chemistry

Reaction Quotient Q vs K Calculator

Compare the reaction quotient Q (computed from current concentrations) to the equilibrium constant K and predict the dir...

basic

5,902 4.7 1 min

Chemistry

Henderson-Hasselbalch Buffer Capacity Calculator

Calculates the buffer capacity β (mol/L per pH unit) using the Van Slyke equation. Maximum buffer capacity occurs at pH...

basic

15,172 4.2 1 min

Showing 133 to 144 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

Newton's Gravitational Force Calculator

Markup and Gross Margin from Cost and Selling Price Calculator

Partition Coefficient (log P) from Concentration Ratio Calculator

Solar Panel Array Area for a Daily-kWh Target Calculator

Typing Speed Words Per Minute Calculator

Half-Life of a Zero-Order Reaction Calculator

Reaction Rate from Concentration Change Calculator

Electronegativity Difference Calculator

Arrhenius Rate Constant Calculator

Bernoulli Equation Calculator

Reaction Quotient Q vs K Calculator

Henderson-Hasselbalch Buffer Capacity Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator