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