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

Hydrostatic Pressure at Depth Calculator

Compute the absolute pressure at a depth h below the surface of a fluid of density ρ, given the pressure at the free sur...

basic

19,963 4.5 1 min

Chemistry

Mole to Mass Conversion Calculator

Convert a number of moles of a substance into a mass in grams using its molar mass: m = n · M. Reports the mass in grams...

basic

11,242 4.7 1 min

Chemistry

Activation Energy from Arrhenius Equation Calculator

Calculates activation energy Ea using the Arrhenius equation at two temperatures: Ea = R·ln(k₂/k₁) / (1/T₁ − 1/T₂). Also...

basic

4,859 4.6 1 min

Physics

Airy Diffraction Resolution Limit (Rayleigh Criterion) Calculator

Compute the Rayleigh angular resolution limit θ_min = 1.22 · λ / D imposed by Airy-disk diffraction through a circular a...

basic

17,432 4.2 1 min

Chemistry

Vapor Density from Molar Mass Calculator

Compute the vapor density of a gas relative to hydrogen (VD = M / 2) from its molar mass, and the corresponding mass den...

basic

1,951 4.0 1 min

Sports / Swimming

Swimming Pace per 100 m / 100 yd Calculator

Converts total swim time and distance into pace per 100 m or 100 yd, and projects splits for any target race distance.

basic

2,359 4.8 1 min

Chemistry

Nuclear Binding Energy from Mass Defect Calculator

Calculates nuclear binding energy BE = Δm·c² from the mass defect Δm = Z·m_p + N·m_n − M_nucleus, expressed in MeV (1 u...

basic

24,226 4.3 1 min

Chemistry / Solutions

Dilution Factor from Stock Concentration and Final Volume Calculator

Compute the dilution factor and final concentration when a stock solution is diluted to a new volume: C₁V₁ = C₂V₂, so C₂...

basic

6,023 4.8 1 min

Chemistry

Electrochemical Equilibrium Constant from Standard EMF Calculator

Calculates the equilibrium constant K = exp(nFE°/RT) from the standard cell EMF E° and number of electrons transferred n...

basic

14,036 4.4 1 min

Finance / Investing

Black–Scholes Option Pricing (Call & Put) Calculator

Calculates European call/put prices: C = S·N(d₁) − K·e^(−rT)·N(d₂); P = K·e^(−rT)·N(−d₂) − S·N(−d₁), using a rational ap...

basic

20,518 3.8 1 min

Physics

Sidereal vs Solar Day Calculator

Compute the sidereal day length given the solar day length and the planet's orbital period: T_sid = T_sol · T_orb / (T_o...

basic

24,017 3.8 1 min

Chemistry

Kp and Kc Equilibrium Conversion Calculator

Converts between Kp (pressure) and Kc (concentration) equilibrium constants using the change in moles of gas Δn and temp...

basic

9,931 4.3 1 min

Showing 397 to 408 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

Hydrostatic Pressure at Depth Calculator

Mole to Mass Conversion Calculator

Activation Energy from Arrhenius Equation Calculator

Airy Diffraction Resolution Limit (Rayleigh Criterion) Calculator

Vapor Density from Molar Mass Calculator

Swimming Pace per 100 m / 100 yd Calculator

Nuclear Binding Energy from Mass Defect Calculator

Dilution Factor from Stock Concentration and Final Volume Calculator

Electrochemical Equilibrium Constant from Standard EMF Calculator

Black–Scholes Option Pricing (Call & Put) Calculator

Sidereal vs Solar Day Calculator

Kp and Kc Equilibrium Conversion Calculator

Reviewed by Dr. Helena Ortiz

Equilibrium Constant Calculator

Length Converter

Combined Gas Law Calculator

Capacitance Calculator

pOH Calculator

Carbon Footprint Calculator