PRB Calculator
Physical Resource Block count for LTE and 5G NR per 3GPP TS 36.101 and TS 38.101.
Each PRB = 12 subcarriers × 14 OFDM symbols (normal CP) = 168 resource elements per slot.
PRB Structure and Formulas
A Physical Resource Block (PRB) is the smallest unit of frequency resource that can be allocated to a user. Each PRB spans 12 consecutive subcarriers and one slot in time.
Resource Elements per PRB per slot = 12 subcarriers × 14 symbols = 168 RE
Total RE per slot = NRB × 168
LTE: BW → NRB (1.4→6, 3→15, 5→25, 10→50, 15→75, 20→100)
NR: NRB depends on SCS (μ) and channel bandwidth
For 5G NR, numerology μ defines the subcarrier spacing (SCS): μ=0 is 15 kHz, μ=1 is 30 kHz, μ=2 is 60 kHz, and μ=3 is 120 kHz (FR2/mmWave). Higher numerology means more slots per 10 ms frame.
Frequently Asked Questions
What is a Physical Resource Block (PRB)?▾
A PRB is the basic scheduling unit in LTE and NR. In LTE, one PRB spans 180 kHz (12 subcarriers × 15 kHz each) and one 0.5 ms slot. In NR, the subcarrier spacing depends on numerology μ, so higher μ values compress more slots into the same 10 ms frame while maintaining the 12-subcarrier structure.
How many PRBs does a 20 MHz LTE carrier have?▾
A 20 MHz LTE carrier has 100 PRBs. Not all 20 MHz is used for data — approximately 10% is guard band on each side, leaving 18 MHz = 100 PRBs × 180 kHz. This pattern applies at all LTE bandwidths.
What is the difference between LTE and NR PRBs?▾
LTE uses a fixed 15 kHz subcarrier spacing across all bands. NR introduces flexible numerology so the same channel bandwidth can carry different numbers of PRBs depending on SCS. A 100 MHz NR carrier at 30 kHz SCS has 66 PRBs, while at 15 kHz SCS it has 132 PRBs.
What are resource elements (RE)?▾
A resource element is the smallest unit of the time-frequency grid: one subcarrier in one OFDM symbol. Each PRB contains 12 × 14 = 168 REs per slot (assuming normal cyclic prefix). Not all REs carry data — some are reserved for reference signals, control channels, and guard periods.