Primary formula
F = k_e x q1 x q2 / r^2.
Physics calculator
Coulomb's Law Calculator
Calculate the electric force magnitude between two point charges from charge values and separation distance.
Last reviewed: July 21, 2026Physics formula engine v3.0.0
Physics calculator
Coulomb's Law Calculator
Enter values, select units and calculate locally. Results use SI internally and show rounded display values.
Decimal.js physics math
Mode
Find electric force from two charges and separation distance.
Result and visual stay hidden until you choose Calculate.
Formula and assumptions
Input assumptions
Separation distance is greater than zero. Charges are treated as point charges. The medium is approximated by the displayed Coulomb constant.
Precision note
Physics calculators convert compatible inputs into SI units before calculating. Decimal.js is used for arithmetic where practical; trigonometric angle factors are rounded for display.
Physics calculation flow
Parse
Read labelled inputs, selected units and calculation mode from the calculator card.
Convert
Convert compatible values to SI base or derived units without calling external services.
Calculate
Apply the selected deterministic mechanics formula and validate against NaN, Infinity and invalid divisors.
Label
Display the result, supporting unit rows, formula steps, warnings and dynamic visual below the input card.
What Coulomb's Law Calculator does
Use this calculator for simplified electrostatics problems involving two point charges.
The calculator is deterministic and runs from manual inputs only. It is a physics formula tool, so it should not be confused with a unit converter that only changes labels after a value is already known.
Formula and variables
F = k_e x q1 x q2 / r^2.
The calculator converts supported units into SI base or derived units for the actual calculation, then formats the result in the selected display unit.
- F is electric force
- k_e is Coulomb's constant
- q1 and q2 are charges
- r is separation distance
Worked examples
Use the examples below to check expected order of operations and unit handling before applying the tool to your own values.
- 1 uC and 1 uC at 1 m gives about 0.0089875517923 N
- 2 uC and -3 uC at 0.5 m gives about 0.2157012430152 N attractive
- Doubling distance reduces force to one quarter.
Unit conversions
Length, time, mass, area, volume, speed, force, pressure, density, frequency, energy and power units reuse the central NexaCalc conversion registry. Acceleration, angle and spring-constant units use the same SI-first convention where applicable.
The displayed conversion rows are supporting context. They do not change the physical assumptions of the selected formula.
Common mistakes
Most errors come from mixing physical quantities that sound similar in everyday language or choosing a unit that belongs to a different dimension.
- Forgetting microcoulomb conversion.
- Using distance not squared.
- Ignoring attraction versus repulsion from charge signs.
Assumptions and limitations
This page is intended for educational and planning calculations, not professional engineering certification.
This calculator uses idealized physics formulas and the input values you provide. Real systems may require additional effects such as friction, drag, rotation, deformation, losses or measurement uncertainty.
- Separation distance is greater than zero.
- Charges are treated as point charges.
- The medium is approximated by the displayed Coulomb constant.
- The calculator does not model extended charge distributions, shielding, dielectric media or quantum effects.
- Very small separations may require a different physical model.
Frequently asked questions
What does Coulomb's Law calculate?
Coulomb's Law Calculator uses F = k_e x q1 x q2 / r^2. The result is calculated from the values and units entered in the form.
What is Coulomb's constant?
Use this calculator for simplified electrostatics problems involving two point charges. Separation distance is greater than zero.
Why is distance squared in Coulomb's Law?
Use this calculator for simplified electrostatics problems involving two point charges. Separation distance is greater than zero.
How do charge signs affect attraction and repulsion?
Use this calculator for simplified electrostatics problems involving two point charges. Separation distance is greater than zero.
What charge units are supported?
Coulomb's Law Calculator converts compatible inputs to SI internally, then displays the selected output unit. F is electric force; k_e is Coulomb's constant; q1 and q2 are charges; r is separation distance.
Can the separation distance be zero?
Coulomb's Law Calculator allows signed results only where the physics quantity can carry direction or reference-sign meaning. Divisors such as time, mass and gravity are validated before calculation.
Does the calculator include dielectric materials?
Coulomb's Law Calculator uses an idealized classroom physics model. The calculator does not model extended charge distributions, shielding, dielectric media or quantum effects.
How is Coulomb's Law different from Magnetic Force Calculator?
Use this calculator for simplified electrostatics problems involving two point charges. Separation distance is greater than zero.
Can this calculator model many charges?
Coulomb's Law Calculator uses an idealized classroom physics model. The calculator does not model extended charge distributions, shielding, dielectric media or quantum effects.
When should I use a field or simulation tool?
Use this calculator for simplified electrostatics problems involving two point charges. Separation distance is greater than zero.
References
- NIST Special Publication 811, Guide for the Use of the International System of Units. Relevance: SI unit symbols and derived-unit naming. Last verified: July 21, 2026. Source.
- BIPM, The International System of Units SI Brochure. Relevance: SI base and derived units used in mechanics, fluids, waves and optics. Last verified: July 21, 2026. Source.
- OpenStax University Physics Volume 1. Relevance: introductory formulas for motion, force, work, energy, momentum, fluids, waves and optics. Last verified: July 21, 2026. Source.
- NIST CODATA internationally recommended values. Relevance: physical constants for electricity, modern physics, gravitation and radiation formulas. Last verified: July 21, 2026. Source.
- OpenStax University Physics Volume 2. Relevance: electric circuits, capacitance, magnetic force and electromagnetic waves. Last verified: July 21, 2026. Source.
- OpenStax University Physics Volume 3. Relevance: photons, nuclear decay and blackbody radiation concepts. Last verified: July 21, 2026. Source.
Physics references verified for SI units, mechanics, fluids, waves, sound and optics formulas on July 21, 2026.
Educational disclaimer
This calculator provides mathematical results from the values, conventions and methods you enter. Verify important academic, engineering or professional work independently.