Electric Field Strength Calculator
Calculate electric field strength from a point charge (E = kQ/r²) or parallel plates (E = V/d).
Covers field direction, superposition, and field line density.
The electric field describes the force that a charged object exerts on other charges in its vicinity. It is a fundamental concept in electrostatics and electrical engineering.
Point Charge Formula (Coulomb’s Law):
E = k × |Q| / r²
Where:
- E = electric field strength (N/C or V/m)
- k = Coulomb’s constant (8.9875 × 10⁹ N·m²/C²)
- Q = charge in coulombs (C)
- r = distance from the charge in meters (m)
Parallel Plates Formula:
E = V / d
Where:
- V = voltage (potential difference) between the plates in volts (V)
- d = distance between the plates in meters (m)
What each variable means:
- Electric field (E): measured in newtons per coulomb (N/C) or volts per meter (V/m). These units are equivalent.
- Charge (Q): the source charge creating the field, in coulombs. 1 coulomb is a very large charge; typical values are in microcoulombs (μC) or nanocoulombs (nC).
- Distance (r): how far from the charge you are measuring the field.
- Voltage (V): the electric potential difference driving the field between plates.
Field strength reference values:
| Source | Electric Field Strength |
|---|---|
| Fair weather atmosphere | ~100 V/m |
| Under a thundercloud | 10,000–30,000 V/m |
| Air breakdown (spark) | ~3,000,000 V/m |
| Inside a capacitor (typical) | 10,000–100,000 V/m |
| Near a Van de Graaff generator | ~1,000,000 V/m |
When to use this calculator:
- Physics and engineering coursework
- Designing capacitors and electrical components
- Understanding electrostatic safety distances
- Calculating forces on charged particles
Practical example: A 1 μC (1 × 10⁻⁶ C) charge creates an electric field of about 9,000 N/C at a distance of 1 meter. At 10 cm, that field increases to 900,000 N/C — showing how rapidly the field strengthens as you get closer.
Tips:
- The electric field from a point charge follows an inverse-square law: doubling the distance reduces the field by 4×.
- Between parallel plates, the field is uniform (constant strength everywhere between the plates).
- Electric field lines point away from positive charges and toward negative charges.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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