Use this electric field calculator to find field strength around a point charge and (optionally) the force on a test charge. It handles common unit conversions automatically, so you can enter microcoulombs, centimeters, and more without manual math.
Point Charge Electric Field Calculator
Formula used: E = k|Q| / r2, where k = 8.9875517923 × 109 N·m2/C2.
What Is an Electric Field?
An electric field describes how a charged particle influences the space around it. If you place another charge in that region, it experiences an electric force. In physics and electrical engineering, electric fields are central to understanding capacitors, electrostatic sensors, dielectric materials, and even lightning behavior.
Core Formula for a Point Charge
For an isolated point charge, the electric field magnitude is:
- E = electric field magnitude (N/C or V/m)
- k = Coulomb constant ≈ 8.9875517923 × 109 N·m2/C2
- Q = source charge (C)
- r = distance from the charge (m)
The field points away from positive charges and toward negative charges.
How to Use This Calculator
Step-by-step
- Enter the source charge value and choose its unit (C, mC, µC, etc.).
- Enter the radial distance from the charge and choose distance units.
- (Optional) Enter a test charge if you also want force output.
- Click Calculate to get electric field magnitude and direction.
If a test charge is included, the calculator also computes force using:
Unit Notes and Conversions
Electrostatics frequently uses very small charges and short distances. The tool converts values internally so the equation is always solved in SI units:
- 1 µC = 1 × 10-6 C
- 1 nC = 1 × 10-9 C
- 1 cm = 1 × 10-2 m
- 1 mm = 1 × 10-3 m
Example
Suppose you have a source charge of +3 µC and want the electric field at 0.25 m.
- Q = 3 × 10-6 C
- r = 0.25 m
- E = k|Q|/r2 ≈ (8.99×109 × 3×10-6) / 0.0625 ≈ 4.31×105 N/C
Because Q is positive, the field direction is away from the source charge.
Common Mistakes to Avoid
- Using distance in centimeters without converting to meters.
- Using r instead of r2 in the denominator.
- Forgetting that electric field direction depends on the sign of the source charge.
- Confusing electric field (N/C) with electric force (N).
Where This Is Useful
This calculator is practical for homework checks, lab prep, and quick engineering estimates in:
- Electrostatics classes
- High-voltage insulation design
- Charge sensor calibration
- Basic semiconductor device intuition