Electric Field Calculator
Get field strength from voltage and gap in metric or imperial.
What it does
Electric field measures volts per distance between charged plates. A thousand volts across ten centimeters gives ten thousand volts per meter. Smaller gaps at the same volts mean stronger fields.
The tool above takes voltage and gap and returns field, kilovolt form, and gap in small units. The defaults 1000 V with 10 cm match the worked example, so the page opens showing 10000 V/m. Switch to imperial for inches.
The form E = V/d suits parallel plates where the field stays nearly uniform in the middle. Edge zones bulge outward and need field solvers. Air breaks near 3 million V/m, so high voltage gaps need clearance and smooth shapes.
Use metric V/m for datasheets and codes. Use V/in for US shop math. Kilovolts per meter compress large numbers: 10000 V/m is 10 kV/m. Gap in mm or mil helps when spacing is tiny.
This page shows the formula, one full hand checked example at 1000 V over 10 cm, a reference table, and practice checks that run through the tool in both unit systems.
How to use
- Pick Metric (cm) or Imperial (in) for gap and field readout.
- Type voltage in volts.
- Type gap in the active unit.
- Read Field strength as the main result.
- Read kilovolt form for large fields.
- Compare gap in mm or mil for shop setup.
Formula
- V
- Voltage across the gap in volts.
- d
- Gap in meters or inches by system.
- E
- Uniform field in V/m or V/in.
Centimeters divide by 100 to meters. Inches multiply by 0.0254 to meters inside. Breakdown in air near 3 MV/m caps practical gaps.
Worked example
Example: 1000 V across 10 cm
Parallel plates hold 1000 V with 10 cm spacing. Find field.
- Write V = 1000 V, gap = 10 cm = 0.1 m.
- Divide: 1000 / 0.1 = 10000 V/m.
- Kilovolts: 10000 / 1000 = 10 kV/m.
- Small gap: 0.1 x 1000 = 100 mm.
- Imperial mirror: 3.94 in gives 253.8 V/in.
- Check: 253.8 V/in x 39.3701 = 9993 V/m, near rounding.
Reference table
| Gap | Field | Note |
|---|---|---|
| 1 cm | 100000 V/m | Strong, near limits |
| 10 cm | 10000 V/m | Example |
| 100 cm | 1000 V/m | Weak |
| 3.94 in | 253.8 V/in | Same as 10 cm |
Limits
- Uniform field only. Edges need solver math.
- DC steady assumed. AC and pulses add frequency terms.
- No breakdown model beyond noting air near 3 MV/m.
- Flat plates assumed. Points and wires concentrate field.
Common mistakes
- Dividing by cm without converting to meters.
- Mixing inches with V/m in one step.
- Reading V/in as V/m, off by 39.37 times.
- Ignoring edge bulge on small plates.
- Pushing air gaps past breakdown strength.
Try it yourself
Quick checks. Answers sit tucked under each question.
500 V across 5 cm?
Field 10000 V/m, 10 kV/m, gap 50 mm.
230 V across 2 cm?
Field 11500 V/m, 11.5 kV/m, gap 20 mm.
Questions
What is electric field?
Volts per distance. 1000 V over 0.1 m is 10000 V/m.
V/m or V/in?
Same physics, different length unit. Multiply V/in by 39.3701 for V/m.
What is breakdown?
Air ionizes near 3 million V/m, so gaps arc above that slope.
Uniform when?
Mid zone of large flat plates. Edges always bulge.
Does shape matter?
Yes. Points raise local field far above V/d.
AC same?
Magnitude form matches at an instant. RMS and peaks need care.