Magnetic Field Strength (H)

H = N · I / l

Quick answer

This calculator solves H = N × I / l for Field Strength. With Number of Turns 0.5, Current 2 A, Path Length 10 mm, the result is 1 A/cm. It solves in 4 directions, so you can enter the values you have and get the one you need.

Calculator

Field Strength (A/m)
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Formula

H = N × I / l

Description

Magnetic field strength (or magnetizing force) H is the MMF per unit length of the magnetic path. It describes how hard the coil drives the magnetic field, independent of the core material. The resulting flux density follows from B = µ₀µr·H, so H is the cause and B is the effect. It is central to reading B–H magnetization curves.

Variables

  • H — Magnetic field strength (A/m)
  • N — Number of turns
  • I — Current (A)
  • l — Magnetic path length (m)

Practical Notes

On a B–H curve the material saturates when increasing H no longer increases B. For a solenoid H = nI where n is turns per metre; for a toroid l is the mean magnetic path length.

Symbols and units

Symbol Meaning Default unit Accepted units
H Field Strength A/m A/m, A/cm, kA/m
N Number of Turns — —
I Current A pA, nA, µA, mA, A, kA
l Path Length mm mm, cm, m, km

Step by step

  1. 1. What you know: Number of Turns 0.5, Current 2 A, Path Length 10 mm
  2. 2. The relation: H = N × I / l
  3. 3. Substitute: N = 0.5, I = 2 A, l = 10 mm
  4. 4. Result: Field Strength = 1 A/cm

Worked examples

Minimum range

Given: Number of Turns 0.025, Current 2 mA, Path Length 0.1 mm

Result: Field Strength = 0.5 A/m

Low range

Given: Number of Turns 0.25, Current 20 mA, Path Length 1 mm

Result: Field Strength = 5 A/m

Typical

Given: Number of Turns 0.5, Current 2 A, Path Length 10 mm

Result: Field Strength = 1 A/cm

High range

Given: Number of Turns 0.8, Current 100 A, Path Length 10 cm

Result: Field Strength = 8 A/cm

Maximum range

Given: Number of Turns 8, Current 1 kA, Path Length 1 m

Result: Field Strength = 8 kA/m

Solving for each variable

Solve for Field Strength

Number of Turns 0.025, Current 2 mA, Path Length 0.1 mm → 0.5 A/m

Solve for Number of Turns

Field Strength 10 A/m, Current 2 mA, Path Length 0.1 mm → 0.5

Solve for Current

Field Strength 10 A/m, Number of Turns 0.025, Path Length 0.1 mm → 40 mA

Solve for Path Length

Field Strength 10 A/m, Number of Turns 0.025, Current 2 mA → 0.005 mm

How Field Strength changes with Number of Turns

Number of Turns (input) Field Strength (result)
0.05 10 A/m
0.125 25 A/m
0.25 50 A/m
0.375 0.75 A/cm
0.5 1 A/cm
0.75 1.5 A/cm
1 2 A/cm
2 4 A/cm
3.5 7 A/cm
5 10 A/cm

The same result in other units

Unit Value
A/m 100
A/cm 1
kA/m 0.1

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Frequently asked questions

How do you calculate Magnetic Field Strength (H)?

Use H = N × I / l. With Number of Turns 0.5, Current 2 A, Path Length 10 mm, Field Strength works out to 1 A/cm.

What is the formula for Magnetic Field Strength (H)?

The formula is H = N × I / l. Magnetic field strength (or magnetizing force) H is the MMF per unit length of the magnetic path.

How do you find Number of Turns when you know the other values?

Rearrange for Number of Turns: with Field Strength 10 A/m, Current 2 mA, Path Length 0.1 mm, Number of Turns is 0.5.

How do you find Current when you know the other values?

Rearrange for Current: with Field Strength 10 A/m, Number of Turns 0.025, Path Length 0.1 mm, Current is 40 mA.

What units does Magnetic Field Strength (H) use?

Field Strength is shown in A/m, A/cm, kA/m. Values are held in SI base units internally, so you can mix prefixes without converting by hand.

Related Concepts

All Magnetics & Transformers formulas →
Transformer EMF Equation Transformer VA Rating Transformer Voltage Regulation Transformer Current Ratio Transformer Copper Loss Transformer Iron (Core) Loss Transformer Turns-per-Volt Magnetic Field Strength (H)

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