UHF Read-Range Estimator
Explore forward-link range with the Friis equation and your own loss budget. This estimates tag activation, not guaranteed system read range.
Use antenna gain at the selected frequency and on the intended mounting surface.
Check the applicable local band and power rules before deployment.
Formula, worked with your inputs
- Wavelength λ = c / f = 3×10⁸ / (915×10⁶) = 0.3277 m
- Reader EIRP = 36 dBm → Pt·Gt = 3981.07 mW
- Tag sensitivity = -24 dBm → required Pr = 3.981 μW
- Tag antenna gain = 2 dBi → Gr = 1.58
- d = (λ / 4π) · √(Pt·Gt·Gr / Pr) = (0.0261) · √(1.585e+6) = 32.82 m (free-space theoretical)
About Friis and this estimator
Friis estimates the forward-link distance at which received power reaches the tag chip's activation threshold. It assumes far-field free-space propagation and matched, aligned antennas. The adjustable loss budget represents additional attenuation or design margin; 6 dB roughly halves the calculated distance. It is an input assumption, not an empirically guaranteed range. The model does not calculate the backscatter return link, reader receiver sensitivity, multipath, interference or tag detuning. Confirm chip sensitivity for the relevant frequency and operating mode, and validate the complete reader, antenna and tagged object in the intended environment. Presets are calculation examples; permitted frequencies and powers depend on the deployment jurisdiction.
Calculate EIRP from conducted power, gain and cable loss. See ETSI EN 302 208 for equipment requirements. Method reviewed 17 October 2026.
FAQ
Does this predict actual read range?
It estimates the forward link only. Reader receive performance, tag antenna matching, orientation and the environment can limit a complete RFID system. Test the final assembly.
What is the difference between EIRP and ERP?
EIRP uses an isotropic reference; ERP uses a half-wave dipole. Add approximately 2.15 dB to ERP to obtain EIRP.
How should I choose the loss budget?
Use measured or justified losses and margin for your application. The 6 dB starting value is an example, not a universal field correction.