What formula does this calculator use?

It uses E = kQ/r², where k = 8.9875 × 10⁹ N·m²/C² is the Coulomb constant, Q is the source charge in coulombs, and r is the distance from the charge in meters. The result E is in volts per meter (V/m), equivalent to newtons per coulomb (N/C).

What does a negative electric field mean?

A negative E value means the field points toward the source charge — indicating a negative source charge that attracts positive test charges. A positive E points away from a positive source charge.

Is V/m the same as N/C?

Yes. Volts per meter (V/m) and newtons per coulomb (N/C) are equivalent units for electric field strength. Both express how much force a unit positive charge would experience per meter of displacement.

Does this apply only to point charges?

Strictly yes — E = kQ/r² is exact for point charges and spherically symmetric charge distributions (by Gauss's law). For extended charge distributions, integration over the charge geometry is required.

The field is undefined at r = 0 (division by zero). The calculator will display an error. In reality, point charges are idealizations — at very small distances the classical model breaks down.

Electric Field Calculator

Name: Electric Field Calculator
Availability: InStock
Author: Nham Vu

Compute the electric field strength at any point from a source charge — or solve for charge or distance — using E = kQ/r².

Electric Field — E = kQ / r²

Select what to solve for, then enter the two known values.

Solve for

Source Charge (Q)

Distance (r)

Result

Enter values and click Calculate

Formula Reference

Electric Field E = kQ / r²

Solve for Q Q = E·r² / k

Solve for r r = √(kQ / E)

Coulomb constant (k) 8.9875 × 10⁹ N·m²/C²

Units (E) V/m ≡ N/C

Summary

Compute the electric field strength at any point from a source charge — or solve for charge or distance — using E = kQ/r².

How it works

Select what you want to solve for: Electric Field (E), Source Charge (Q), or Distance (r).
Enter the two known values with their preferred units.
Click Calculate to apply E = kQ/r².
Read the result displayed in the most convenient unit with scientific notation.
Check the "Also expressed as" section for alternative unit conversions.
Click Reset to start a fresh calculation.

Use cases

Solve electrostatics problems in physics courses.
Verify the field strength around charged conductors or particles.
Determine how far from a charge you need to be to achieve a target field.
Explore how field strength falls off with the inverse-square law.
Cross-check hand calculations for lab reports and homework.
Teach or study the relationship between charge, distance, and field intensity.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu