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RF Link Budget Calculator

Compute RF link budget: FSPL, path loss with antenna gains and misc loss, received power, and optional margin above sensitivity. Extends Free-Space Path Loss.

Instant result
Result
—

Enter values to calculate.

Inputs—
Mode—
Formula—
Trust summary CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance
Input interpretation
Enter values to calculate.
Result
—
Assurance
Engineering
Declared partition coverage
PASS · 3/3 declared partitions (isotropic, with-gains, invalid-domain) · Matrix
Known limitations
  • Free-space path; u_* GUM deferred from this CVP wave
  • Core CVP does not include live graph, viewport, or pointer interaction.
Model
Free-space link budget: FSPL, path loss, Pr, optional margin; optional expanded uncertainty on Pr.
Scope
Ideal free space; isotropic FSPL reference
Verification
Engine tested · Source checked · v1.1.1 · CVP VERIFIED · CVP protocol 1.0.0-proposed · Engineering assurance· View Manifest · CVP overview · Specification
Versions
Calculation 1.1.1 · CVP protocol 1.0.0-proposed · Evidence 2026-09-11.schema-coverage-u
Verification revision
2026-09-11.schema-coverage-u · 5/5 property · digest da256fa94e72
Legacy regression
12/12 tests · Production surface contract 6/6
Reference
O1 model · O2 expected_values · O2 numerical_behavior
Interfaces
PASS · UI (SSR) / REST / MCP — ui-ssr is query-result HTML, not a live browser session.
Supplemental domain review
Internal · Pass · electrical-engineer
Named expert review
Not performed
CVP suite
2/2 golden · 5/5 CVP boundary · 3/3 invalid · 5/5 property · 1/1 cross-interface · 6/6 CVP contract · Manifest
Sources
  • Friis transmission equation — Free-space link
  • ITU-R P.525 — Free-space attenuation
Sources
Evidence
2 legacy golden · 5 legacy boundary · legacy regression suite · 2/2 oracle-backed golden · 3/3 invalid · Artifact integrity PASS · CalculatorX electrical review
This calculator CURRENT · Public schema 1.1.1 matches · Semantic contract ✓ · Production attested · Public/cache ✓ · Origin ✓
Semantic contract
PASS
Full verification

Manifest identity, reference classes, interfaces, suite, and production records.

Formulas

Core equations used by this calculator.

FSPLFSPL = 20·log10(d)+20·log10(f)+20·log10(4π/c)
Received powerPr = Pt − (FSPL − Gt − Gr + L)
iIdeal free space. Extends electrical.rf.fspl; no rain fade or multipath.

How to use

1

Enter transmit power, distance, and frequency

Pt, range, and f set free-space path loss.

2

Optional: enter antenna gains and extra losses

Gt, Gr, and cable/other loss adjust received power.

3

Optional: enter sensitivity to check margin

If sensitivity is provided, link margin = Pr − S is shown.

4

Optional uncertainties

Enter u(Pt), u(d), u(f), u(Gt), u(Gr), and/or u(L) to show Pr ± U (k=2 by default) via the Uncertainty Engine.

Example calculations

Common configurations with formula and result.

ϟ

20 dBm · 1 km · 2.4 GHz

Isotropic · S=-90 dBm

Pr = Pt − FSPL
Pr ≈ -80.05 dBm · margin ≈ 9.95 dB
ϟ

With Pt & distance uncertainty

Same link · u(Pt)=0.5 dB · u(d)=50 m · k=2

GUM sensitivity on Pr
Pr ≈ -80.05 ± 1.32 dBm

RF Link Budget calculator specification

Version 1.1.1 · Engine tested · Supplemental domain review · Internal · 2026-08-10

Calculation status

Review policy · Evidence · Reviewed by CalculatorX electrical review (electrical-engineer)

Definition
A simple free-space link budget: FSPL from Friis, path loss = FSPL − Gt − Gr + L, Pr = Pt − path loss, and optional margin = Pr − S.
What it calculates
Free-space link budget: FSPL, path loss, Pr, optional margin; optional expanded uncertainty on Pr.
Inputs
  • Pt_dBm, d_m > 0, f_Hz > 0
  • Optional Gt_dBi, Gr_dBi, L_dB ≥ 0, S_dBm
  • Optional u_Pt_dBm, u_d_m, u_f_Hz, u_Gt_dBi, u_Gr_dBi, u_L_dB ≥ 0; optional uncertainty_k (default 2) or confidence
Outputs
  • fspl_dB
  • path_loss_dB
  • Pr_dBm
  • margin_dB?
  • wavelength_m
  • uncertainty?
  • …
Formula
Pr = Pt − (FSPL − Gt − Gr + L); margin = Pr − S; optional U=k·u_c(Pr)
Assumptions
  • Ideal free space; isotropic FSPL reference
  • When u_* are set, first-order GUM sensitivity with independent inputs (no ρ on this page)
Units
  • dBm, m, Hz, dBi, dB
Boundary conditions
  • Missing Pt/d/f → MISSING_REQUIRED_INPUT
  • L_dB < 0 → VALUE_MUST_BE_NON_NEGATIVE
  • uncertainty_k without any u_* → INVALID_INPUT
Example
Pt=20 dBm, 1 km, 2.4 GHz, S=-90 → Pr≈-80.05 dBm
Validation cases

3 published on this page · 12/12 tests · Production surface contract 6/6 · View evidence

  • Pt=20, d=1km, f=2.4GHz, S=-90 → Pr≈-80.052, margin≈9.948
  • Gt=Gr=6 → path_loss = fspl − 12
  • u_Pt_dBm=0.5, u_d_m=50 → Pr≈-80.052 with uncertainty.U≈1.32 (k=2)
Sources
  • Friis transmission equation — Free-space link
    Supports: FSPL and received-power form
  • ITU-R P.525 — Free-space attenuation
    Supports: Standard FSPL formulation
Last reviewed
2026-08-10
Reviewed by
CalculatorX electrical review (electrical-engineer)
Calculation version
1.1.1

Background

Interpretation and common distinctions.

Build a simple RF link budget on Friis FSPL with gains, misc loss, and optional sensitivity margin. Optional standard uncertainties compose an expanded interval on Pr via the Uncertainty Engine.

Default: 20 dBm · 1 km · 2.4 GHz · S=-90 → Pr ≈ -80.05 dBm.

Agent / API notes

Capability id: electrical.rf.link_budget · tool id: rf-link-budget · alias link-budget · pin calculation_version: 1.1.1.

When any u_* is set, the engine attaches uncertainty: { u_c, U, k, contributions, … } on Pr_dBm. Empty u_* preserves the 1.0.0 nominal-only fields.

Other calculators in this family: Antenna Length Calculator, Cascaded Noise Figure Calculator, Coax Impedance Calculator, dBm to Watts Calculator, Free-Space Path Loss Calculator, L-section LC Match Calculator, Receiver Sensitivity Calculator, Reflection Coefficient to Impedance Calculator . Explore all RF & Microwave.

→ Antenna Length Calculator Compute dipole (λ/2) or monopole (λ/4) antenna length from frequency and an empirical length factor. Runs locally in your browser. › → Cascaded Noise Figure Calculator Compute cascaded noise figure and total gain for a multi-stage RF chain using the Friis formula. Add, remove, or reorder stages. Runs locally in your browser. › → Coax Impedance Calculator Compute coaxial characteristic impedance Z0 from shield inner diameter D, center-conductor diameter d, and dielectric εr. Ideal TEM, μr≈1. Runs locally in your browser. › → dBm to Watts Calculator Convert dBm ↔ watts and dBm ↔ milliwatts with hard validation. Canonical Unit Engine for RF power. › → Free-Space Path Loss Calculator Compute free-space path loss FSPL = 20·log10(d·f) + 20·log10(4π/c) from distance and frequency, with optional antenna gains. Runs locally in your browser. › → L-section LC Match Calculator Narrowband real RL→Z0 L-section match with dual LP/HP solutions. Runs locally in your browser. › → Receiver Sensitivity Calculator Estimate MDS: S = −174 + NF + 10·log10(BW) + SNR_min (dBm). Runs locally in your browser. › → Reflection Coefficient to Impedance Calculator Convert complex Γ ↔ normalized z (Cartesian or polar Γ). Reports VSWR and return loss. Runs locally in your browser. ›
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Frequently asked questions

Key distinctions behind the calculation.

How does this relate to FSPL?

FSPL is computed with the same Friis formula as the FSPL calculator, then gains and misc loss adjust path loss and received power.

What is margin?

If you enter sensitivity S_dBm, margin = Pr − S. Positive means the received level exceeds the sensitivity floor in this ideal model.

How do optional uncertainties work?

Provide standard uncertainties u_Pt_dBm, u_d_m, u_f_Hz, u_Gt_dBi, u_Gr_dBi, and/or u_L_dB. The engine composes them with GUM sensitivity on Pr_dBm via engineering.uncertainty.propagate (default k=2). Distance and frequency use SI units (m, Hz) for both the value and its uncertainty.