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

Chemistry

Fugacity Coefficient from van der Waals Equation Calculator

Calculates the van der Waals fugacity coefficient φ = exp[(b/(Vm−b)) − (2a/(RT·Vm))], where a and b are VdW constants, f...

Basic

8,591 4.9 1 min

Physics

Critical Angle for Total Internal Reflection Calculator

Compute the critical angle of incidence at which light travelling from a denser medium (n₁) into a rarer medium (n₂) und...

Basic

15,891 4.3 1 min

Physics / Mechanics

Simple Harmonic Motion Period (Mass-Spring) Calculator

Compute the period and frequency of a mass-spring oscillator undergoing simple harmonic motion from the mass m and sprin...

Basic

810 4.6 1 min

Physics

Bernoulli Orifice Flow Discharge Calculator

Calculates volumetric flow rate through a circular orifice using Bernoulli's equation with a discharge coefficient, head...

Basic

20,051 4.9 1 min

Finance

Economic Order Quantity (EOQ) Calculator

Calculates the economic order quantity (EOQ) to minimise total inventory costs from annual demand, ordering cost, and ho...

Basic

10,875 4.5 1 min

Chemistry

Standard Cell Potential from Half-Reaction Potentials Calculator

Calculates the standard cell potential E°_cell = E°_cathode − E°_anode from the standard reduction potentials of two hal...

Basic

10,129 4.1 1 min

Chemistry

Percent Recovery from Extraction Calculator

Compute the percent recovery of a substance from a purification or extraction step from the recovered (final) mass and t...

Basic

24,489 4.2 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

12,634 4.8 1 min

Finance

Reorder Point with Safety Stock Calculator

Calculates the reorder point ROP = average demand per day × lead time days + safety stock. Safety stock = z × σ_demand ×...

Basic

7,759 4.6 1 min

Chemistry

Half-Cell Potential with Nernst Equation Calculator

Calculates the actual electrode potential E = E° − (0.05916/n)·log₁₀(Q) at 298 K using the Nernst equation, given the re...

Basic

1,069 4.4 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

24,732 4.1 1 min

Sports

Soccer Expected Goals xG Simple Model Calculator

Estimates expected goals (xG) for a shot in soccer/football using a simplified exponential model based on shot distance...

Basic

24,507 4.5 1 min

Showing 517 to 528 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

Fugacity Coefficient from van der Waals Equation Calculator

Critical Angle for Total Internal Reflection Calculator

Simple Harmonic Motion Period (Mass-Spring) Calculator

Bernoulli Orifice Flow Discharge Calculator

Economic Order Quantity (EOQ) Calculator

Standard Cell Potential from Half-Reaction Potentials Calculator

Percent Recovery from Extraction Calculator

Arrhenius Rate Constant Calculator

Reorder Point with Safety Stock Calculator

Half-Cell Potential with Nernst Equation Calculator

Expected Value of a Discrete Distribution Calculator

Soccer Expected Goals xG Simple Model 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