This electric field calculator finds field strength two ways: from a point charge (E = kQ/r²) and between parallel plates (E = V/d) — with the force the field would exert on a test charge.

Electric field E –
Force on the test charge F = qE –

The Field: Force-Per-Charge, Mapped Through Space

The law underneath is our Coulomb’s Law Calculator — E is just Coulomb’s force divided by the test charge, which is why the test charge’s own size cancels out. Part of our Physics Calculators collection.

Worked Examples (Verified)

  • Q = 5 µC at r = 0.3 m (defaults): E = kQ/r² = 4.99 × 10⁵ N/C pointing away from the charge; a 1 µC test charge feels 0.499 N
  • 12 V across a 2 mm gap (plate mode): E = 12/0.002 = 6,000 V/m, uniform between the plates — the geometry inside capacitors and CRT/electron optics
  • Inverse-square honesty: doubling r quarters E — at 0.6 m the same charge gives 1.25 × 10⁵ N/C; fields fade fast, which is why plate geometry (no distance decay inside) is engineering’s favorite trick

Field Discipline

  • Units N/C and V/m are the same unit wearing two hats — force-per-charge and potential-per-distance; both appear on datasheets.
  • Direction: field vectors point away from positive charges, toward negative ones; E’s sign here is reported as magnitude — direction follows the charge’s sign.
  • Superposition: fields from multiple charges add as VECTORS at each point — two equal opposite charges cancel on their perpendicular bisector, reinforce along the axis.
  • Air breaks down near 3 × 10⁶ V/m — the silent ceiling behind spark gaps, lightning and why high-voltage gear is big.

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Frequently Asked Questions

How do you calculate the electric field of a point charge?

E = k|Q|/r² with k = 8.988 × 10⁹ N·m²/C². Example: 5 µC at 0.3 m → 4.99 × 10⁵ N/C. The field depends only on the source charge and distance — not on whatever charge you later place there. This calculator also handles the parallel-plate case E = V/d.

What is the electric field between parallel plates?

E = V/d, uniform (away from edges): 12 V across 2 mm gives 6,000 V/m. Uniformity is the point — charged particles between plates feel the same force everywhere, which is why the setup drives displays, sensors and particle steering.

Are N/C and V/m really the same?

Yes: 1 N/C = 1 V/m, provable from W = F·d and V = W/q. Field-as-force-per-charge and field-as-potential-gradient are one quantity — E = −ΔV/Δx in general, of which the plate formula is the constant case.

How does the field relate to force?

F = qE: a charge q placed in field E feels force qE (direction flipped for negative q). This page reports both — the field from your source, and the force on a test charge you specify.

Why does the point-charge field fall as 1/r²?

Geometry: the field’s “influence” spreads over a sphere of area 4πr², so its density dilutes with r² — the same reason gravity and Coulomb force share the inverse-square form, and the pattern Gauss’s law formalizes.

Is this electric field calculator free?

Yes — free, instant, no sign-up.