RF Link Budget Calculator
Calculate RF received power, EIRP, receiver sensitivity margin, required transmit power, and maximum allowable path loss from a configurable wireless link budget.
RF-005 is the general budget tool. RF-004 only calculates free-space path loss, while RF-012 is reserved for ideal Friis received-power calculations.
Engineering tool
RF Link Budget Calculator
Calculate received power, EIRP, receiver sensitivity margin, required transmit power, maximum allowable path loss and compare two RF link budgets.
Result console
- Transmit Power
- 20 dBm100 mW
- EIRP
- 23 dBm
- Total Gains
- 10dB
- Total Losses
- 107dB
- Received Power
- -77 dBm19.952623 pW
- Receiver Sensitivity
- -90 dBm
- Raw Link Margin
- 13dB
- Available Margin
- 3dB
- Link Status
- Limited to Moderate Margin
- Formula Used
- Prx = Ptx + Gtx + Grx - Ltx - Lrx - Lpath - Lother
Link status is a general engineering description, not a reliability guarantee. Real margin depends on fading, modulation, coding, data rate, mobility, interference, antenna orientation, deployment conditions, regulation and manufacturer limits.
Formula reference
RF Link Budget Formulas
Absolute power terms use dBm or dBW. Gains, losses, antenna gain, and margin use dB or dBi.
EIRP = Ptx - Ltx + GtxPrx = Ptx + Gtx + Grx - Ltx - Lrx - Lpath - LotherMraw = Prx - SensitivityMavailable = Mraw - MrequiredPtx,required = Sensitivity + Mrequired + Ltx - Gtx + Lpath + Lother - Grx + LrxLpath,max = Ptx - Ltx + Gtx + Grx - Lrx - Lother - Sensitivity - MrequiredVariable definitions
- Ptx
- transmitter output power as an absolute power level
- Prx
- receiver input power as an absolute power level
- EIRP
- equivalent isotropic radiated power
- Gtx and Grx
- transmit and receive antenna gain in dBi
- Ltx and Lrx
- transmit-side and receive-side losses entered as positive dB values
- Lpath
- propagation path loss in dB
- Lother
- summed additional losses such as polarization, building, foliage, rain or implementation loss
- Sensitivity
- receiver sensitivity for the chosen modulation, rate and bandwidth
- Mraw
- received power above sensitivity
- Mrequired
- required fade or design margin
- Mavailable
- margin remaining after the required design allowance
Worked Examples
Basic link budget
20 dBm - 2 dB + 5 dBi - 100 dB - 3 dB + 5 dBi - 2 dB = -77 dBm received power. Raw margin is 13 dB and available margin after 10 dB requirement is 3 dB.
Negative link margin
10 dBm, 2 dB Tx loss, 2 dBi Tx gain, 115 dB path loss, 5 dB other loss, 2 dBi Rx gain, and 2 dB Rx loss gives -110 dBm received power and -10 dB raw margin against -100 dBm sensitivity.
High-gain antennas
30 dBm with 15 dBi antennas on both ends, 130 dB path loss, 2 dB other loss and 1 dB loss per side gives 44 dBm EIRP and -74 dBm received power.
Required transmit power
Sensitivity -100 dBm with 10 dB required margin, 120 dB path loss, 3 dB other loss, 5 dBi antennas and 2 dB losses per side requires 27 dBm transmitter output and 30 dBm EIRP.
Maximum allowable path loss
20 dBm Tx power, 5 dBi antennas, 2 dB loss per side, 3 dB other loss, -100 dBm sensitivity and 10 dB margin allows 113 dB path loss.
Power unit equivalence
1 W transmitter output equals 30 dBm and must produce the same received power as 30 dBm with identical gains and losses.
Cable-loss improvement
Reducing transmit loss from 3 dB to 1 dB and receive loss from 3 dB to 1 dB improves received power by 4 dB.
Antenna-gain improvement
Changing both antennas from 2 dBi to 8 dBi improves received power by 12 dB when other terms are unchanged.
Receiver sensitivity comparison
At the same -85 dBm received power, -90 dBm sensitivity gives 5 dB raw margin while -100 dBm sensitivity gives 15 dB raw margin.
Required margin independence
Changing required margin from 5 dB to 15 dB does not change received power or raw margin; it only reduces available margin by 10 dB.
Engineering Notes
- A link budget is the algebraic sum of all link gains and losses.
- Transmit power and received power are absolute powers, usually handled in dBm.
- Antenna gain and losses are relative quantities in dB or dBi.
- Loss inputs should be positive values; the calculator subtracts them internally.
- EIRP is not the same as transmitter port output power.
- Receiver sensitivity depends on modulation, data rate, bandwidth, coding and error-rate target.
- Required fade margin is a design reserve, not an extra physical loss deducted from received power.
- Maximum allowable path loss is not coverage distance; use RF-004 or another propagation model for distance.
- A positive link margin does not prove regulatory compliance, RF exposure compliance, or reliable field performance.
- Use datasheets, measured losses and verified propagation assumptions for critical parameters.
Common Mistakes
- Treating dB as absolute power.
- Treating dBi as transmitter output power.
- Forgetting to subtract cable or connector loss.
- Entering loss as a negative value and accidentally adding it.
- Ignoring receive-side cable loss.
- Treating FSPL as a complete link budget.
- Ignoring receiver sensitivity test conditions.
- Subtracting required fade margin from received power instead of from raw margin.
- Assuming positive margin guarantees a reliable connection.
- Ignoring polarization mismatch, body loss, building penetration, antenna direction and regulatory EIRP limits.
Support reference
FAQ
What is an RF link budget?
An RF link budget is the algebraic sum of transmit power, antenna gains, propagation loss, cable losses, implementation losses and receiver sensitivity margin.
How do I calculate received RF power?
Use Prx = Ptx + Gtx + Grx - Ltx - Lrx - Lpath - Lother after converting absolute powers to dBm and entering gains and losses in dB.
What is EIRP?
EIRP is equivalent isotropic radiated power. It is calculated as transmitter output power minus transmit-side loss plus transmit antenna gain in dBi.
What is receiver sensitivity?
Receiver sensitivity is the minimum receiver input level for a defined modulation, data rate, bandwidth, coding, temperature and error-rate target.
What is link margin?
Raw link margin is received power minus receiver sensitivity. Available margin subtracts the required fade or design margin from that raw margin.
How much link margin is enough?
There is no universal value. Required margin depends on propagation variability, mobility, reliability target, interference, modulation, coding, data rate, antenna installation and application requirements.
What is maximum allowable path loss?
Maximum allowable path loss is the largest path-loss value the budget can tolerate while meeting sensitivity and required margin. It is not a distance by itself.
Does link budget include interference?
This calculator does not model interference directly. You can include implementation or interference allowance in Other Losses, but detailed interference analysis requires a separate system model.
What is the difference between FSPL and link budget?
FSPL is only one propagation loss term. A link budget also includes transmit power, antenna gains, cable losses, receiver sensitivity, other losses and margin.
Can positive link margin guarantee reliability?
No. Positive calculated margin does not guarantee reliable, legal or safe operation. Real links must be verified against environment, regulation, hardware and deployment conditions.
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Future Engineering Guide Topics
How to Build an RF Link Budget
In_DevelopmentUnderstanding EIRP
In_DevelopmentReceiver Sensitivity and Link Margin
In_DevelopmentHow Antenna Gain Affects Wireless Range
In_DevelopmentCable Loss in RF Systems
In_DevelopmentFade Margin for Wireless Links
In_DevelopmentFree-Space Path Loss Explained
In_DevelopmentDisclaimer
This calculator provides first-pass RF link-budget estimates. It does not verify regulatory compliance, RF exposure compliance, antenna installation, transmitter hardware limits, receiver overload, interference environment, or field reliability.