Calculate the magnitude of the electric field from a point charge. Enter the charge magnitude and distance to calculate the electric field at that distance (in free space/air). This calculator can also determine the charge magnitude or distance given the electric field magnitude and one of those values.

Electric Field Calculator

Pick a method below. For the first three methods, fill any 2 fields to solve the missing one.
Uses Coulomb’s law: E = k · |Q| / (εr · r²) (magnitude). Direction: away from +Q, toward −Q.
Use εr = 1 for vacuum/air. Water is ~80 (approx.).
Uniform field approximation between parallel plates: E ≈ |V| / d.
Best for large, parallel plates (edge effects ignored).
Definition: E = F / |q| (magnitude). If q is negative, field direction is opposite the force direction.
Net field at the observation point x = 0 from charges on a line: E = Σ [ k·Qi·(−xi) / |xi|³ ]. Enter up to 4 charges (leave rows blank to ignore). Position xi: + is to the right, − is to the left.
Charges (Qi) and positions (xi)
Tip: A charge at x > 0 (to the right) pushes a positive test charge left; a negative charge pulls it right.
Results
Electric Field
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Equivalent
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Electric Field Formula

The formula used to calculate the magnitude of an electric field from a point charge at a given distance (in free space/air) is as follows:

 E = k * |Q| / r^2
  • Where E is the magnitude of the electric field (in N/C or V/m)
  • k is Coulomb’s constant (approximately 8.9876 × 10^9 N·m²/C²)
  • Q is the charge magnitude
  • r is the distance from the charge to the point where the field is evaluated

To calculate the magnitude of an electric field from a point charge, divide the charge magnitude by the distance squared, then multiply the result by Coulomb’s constant.

Electric Field Definition

An electric field is a vector field that assigns to each point in space the electric force per unit positive test charge, E = F/q.

Electric fields are produced by electric charges (point charges or continuous charge distributions). At the atomic scale, electric attraction between negatively charged electrons and the positively charged nucleus (together with quantum effects) underlies the structure of atoms and chemical bonding. Electric fields and magnetic fields are part of the overarching electromagnetic interaction.

The following example will show you how you can calculate the electric field of a point charge.


How to calculate the electric field from a point charge

  1. First, determine the charge magnitude

    This is typically measured or given. For this example, assume a charge magnitude of 1 microcoulomb (1 × 10⁻⁶ C), which is a small static charge in many situations.

  2. Next, determine the distance from the charge

    Choose or use the given distance from the charge to the point where you want the field. For this example, let the distance be r = 5 meters.

  3. Finally, enter the information into the formula

    Use E = k|Q|/r². For the example: E = (8.9876 × 10⁹) × (1 × 10⁻⁶) / (5²) ≈ 3.60 × 10² N/C (≈ 360 V/m). You can also use the calculator above.

  4. Analyze the results

    Check units (N/C or V/m) and that the magnitude is reasonable. The field points radially outward for a positive charge and inward for a negative charge.

FAQ

What is an electric field?

An electric field is a vector field that gives the electric force per unit positive test charge at each point in space (E = F/q).