EMCEasyEngineering tools that explain
Home/Calculators/Wavelength and Critical Dimensions
EMC Design

Wavelength and Critical Dimensions Calculator

Calculate wavelength and 1/4λ, 1/10λ, and 1/20λ dimensions from frequency and medium properties.

FORMULAv1.1.0
INPUT PARAMETERS

Enter propagation parameters

Frequency must be greater than zero. In air, εᵣ and μᵣ are usually approximated as 1.

CALCULATION RESULT

Calculation result

Calculated locally
∿

Enter the parameters and run the calculation to see results and model assumptions here.

FORMULA & TRACEABILITY

Formulas and applicability

Formulas, variables, and model boundaries are published. References last reviewed on 2026-08-30.

4 formulas · 2 references
CORE EQUATIONS

Core equations

These equations directly produce the primary results and define the tool’s core model.

2
F01

Phase velocity in a uniform medium

vₚ = c / √(εᵣ μᵣ)

Estimate phase velocity from the speed of light in vacuum and the medium’s relative permittivity and permeability.

vₚ
Phase velocitym/s
c
Speed of light in vacuum (exactly 299,792,458)m/s
εᵣ
Relative permittivity1
μᵣ
Relative permeability1
Applicability
  • A uniform, isotropic, approximately lossless medium
  • εᵣ and μᵣ are real-valued and may be treated as constant near the target frequency
F02

Frequency and wavelength

λ = vₚ / f

Wavelength equals propagation velocity divided by frequency; in free space, vₚ = c.

λ
Wavelengthm
vₚ
Phase velocitym/s
f
FrequencyHz
Applicability
  • Use phase velocity and frequency for the same medium
DERIVED & CONVERSION

Derived and conversion equations

Derive units, levels, and supporting engineering quantities from the core values.

2
F03

Period

T = 1 / f

The reciprocal of frequency is the time for one complete cycle.

T
Periods
f
FrequencyHz
Applicability
  • Steady-state single-frequency analysis or an estimate at the target frequency
F04

Phase constant

β = 2π / λ

Describes phase change per unit length along the direction of propagation.

β
Phase constantrad/m
λ
Wavelengthm
Applicability
  • Uniform propagation medium
  • Use the wavelength in the applicable medium
REFERENCES

References

01BIPM · SI Brochure, 9th editionThe International System of Units (SI): metre2019 (updated 2026) · Defines the exact speed of light in vacuum: c = 299,792,458 m/s.
02ITU-T · Recommendation K.91Guidance for assessment of human exposure to RF electromagnetic fields2024 · Gives λ = v/f and explains that a medium reduces propagation velocity.
Engineering use notice

Results use the models and assumptions shown on this page for design estimates and pre-compliance risk review. Complex structures, dispersion, near-field coupling, and test setup can cause significant deviation.

FAQ

Frequently asked questions

What is the wavelength formula?

λ = v / f, where v = c = 299,792,458 m/s in free space. For example, 300 MHz corresponds to λ ≈ 1 m.

What are the 1/4λ and 1/20λ dimensions used for?

1/4λ marks the cable and aperture resonance length; 1/10λ–1/20λ is a common early-design reference for shield apertures, beyond which leakage increases significantly.

Why is the wavelength shorter in a dielectric?

Phase velocity drops to v = c / √(εᵣ·μᵣ), so the wavelength shortens proportionally. On FR4 (εᵣ ≈ 4.3), microstrip wavelength is roughly half of free space.

PRE-COMPLIANCE SUPPORT

Need accredited testing or pre-compliance support?

These tools support design-stage estimates. For accredited EMC testing, compliance decisions, and troubleshooting, contact us.

Contact us