5G NR Physical Resource Block (PRB) Calculator
Dimension 3GPP 5G New Radio maximum active Physical Resource Blocks (PRBs), active OFDMA subcarriers, Resource Elements (REs) per slot, and transmission bandwidth configurations across FR1 and FR2 numerologies per 3GPP TS 38.101-1 and TS 38.101-2.
Resource Grid Configuration
Resource Blocks & RE Capacity
Physical Resource Block (PRB) Architecture in 3GPP 5G New Radio
In 3GPP Fifth Generation New Radio (5G NR), the Physical Resource Block (PRB) serves as the fundamental scheduling building block for baseband channel estimation, resource allocation, and user throughput optimization. As formally defined in 3GPP TS 38.211, one PRB is strictly composed of exactly 12 consecutive subcarriers in the frequency domain, irrespective of the operating numerology or frequency range.
This represents an intentional architectural departure from legacy 4G LTE. In LTE, the air interface was rigid and non-scalable: subcarrier spacing was locked to 15 kHz, fixing the bandwidth of every Physical Resource Block to exactly 180 kHz (12 subcarriers × 15 kHz) and binding each slot to a static 0.5 ms time duration (7 symbols). In 5G NR, numerology scales exponentially as Δf = 2μ × 15 kHz, where μ ∈ {0, 1, 2, 3, 4}. Consequently, the physical bandwidth spanned by a single 5G PRB scales dynamically:
This formulation results in PRB bandwidths of:
- 15 kHz SCS (μ=0): 12 × 15 kHz = 180 kHz per PRB (matching legacy LTE).
- 30 kHz SCS (μ=1): 12 × 30 kHz = 360 kHz per PRB (global mid-band / C-Band standard).
- 60 kHz SCS (μ=2): 12 × 60 kHz = 720 kHz per PRB (high-speed vehicular & dense urban).
- 120 kHz SCS (μ=3): 12 × 120 kHz = 1,440 kHz (1.44 MHz) per PRB (FR2 mmWave).
Common Resource Blocks (CRB), Point A & BWP Alignment
To maintain coherent frequency coordination across diverse carrier configurations, 5G NR introduces the Common Resource Block (CRB) grid. Unlike LTE, where resource block numbering was relative to the carrier center frequency, 5G NR establishes a global absolute reference point designated as Point A.
Point A represents an absolute physical RF reference frequency (expressed via absolute radio frequency channel numbers or ARFCN) that serves as the center of subcarrier 0 of Common Resource Block 0 (CRB 0). All user-specific resource grids, Bandwidth Parts (BWPs), and Synchronization Signal Blocks (SSB) are referenced via an offset integer from Point A.
Through Bandwidth Part (BWP) adaptation, a gNodeB can dynamically instruct a mobile device (UE) to narrow its operational RF receiver window from a full 100 MHz wideband carrier (273 PRBs) down to an energy-efficient 20 MHz BWP (51 PRBs) during periods of low traffic demand. This dynamic adaptation yields substantial battery conservation without tearing down active RRC connections.
Resource Element (RE) Granularity and Symbol Overhead
The atomic unit of the 5G NR physical layer is the Resource Element (RE), which represents exactly one subcarrier in the frequency domain spanning one OFDM symbol duration in the time domain. Under a standard slot structure with Normal Cyclic Prefix, each slot contains exactly 14 OFDM symbols. Therefore, the total number of REs contained within a single PRB over one slot is:
When Extended Cyclic Prefix is employed (μ=2, 60 kHz SCS), each slot is shortened to 12 OFDM symbols to accommodate severe multipath delay spreads, reducing slot density to 144 REs per PRB. Within this grid, REs are systematically allocated between user payload data (PDSCH in the downlink, PUSCH in the uplink) and critical PHY layer overheads:
- Demodulation Reference Signals (DMRS): Channel estimation symbols embedded directly within scheduled PRBs.
- Phase Tracking Reference Signals (PTRS): Essential in FR2 mmWave to track and compensate for oscillator phase noise.
- Channel State Information Reference Signals (CSI-RS): Sounding signals for beamforming weight calculation and CQI/PMI/RI reporting.
- Physical Downlink Control Channel (PDCCH): Carrying Downlink Control Information (DCI) for dynamic scheduling grants.
The Physics of 3GPP TS 38.101 Transmission Bandwidth Limits
The maximum allowable PRB allocations codified in 3GPP TS 38.101-1 (Table 5.3.2-1) and TS 38.101-2 (Table 5.3.2-1) represent an optimized balance between spectral efficiency and RF transceiver filter feasibility.
For example, in a 100 MHz C-Band carrier with 30 kHz SCS, 3GPP sets the maximum allocation at exactly 273 PRBs. The physical active transmission bandwidth occupies:
This leaves an intentional 1.720 MHz margin (860 kHz on each channel boundary) as an unmodulated guardband. This guardband allows commercial analog surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters to roll off without violating 3GPP Adjacent Channel Leakage Ratio (ACLR) limits. If 274 PRBs were scheduled, the transmission bandwidth would expand to 98.64 MHz, compressing the edge guardbands to only 680 kHz and causing severe out-of-band emissions into adjacent spectrum licenses.
3GPP TS 38.101 PRB Allocation Reference Table
The table below documents standardized maximum active PRBs (NPRB), Resource Elements per slot (Normal CP), and active transmission bandwidth across all standardized 3GPP channel bandwidths and numerologies:
| Channel BW | SCS 15 kHz (μ=0) | SCS 30 kHz (μ=1) | SCS 60 kHz (μ=2) | SCS 120 kHz (μ=3) | Max REs/Slot (Normal CP) | Transmission BW |
|---|---|---|---|---|---|---|
| 5 MHz | 25 PRBs | 11 PRBs | N/A | N/A | 4,200 REs | 4.50 MHz / 3.96 MHz |
| 10 MHz | 52 PRBs | 24 PRBs | 11 PRBs | N/A | 8,736 REs | 9.36 MHz / 8.64 MHz |
| 15 MHz | 79 PRBs | 38 PRBs | 18 PRBs | N/A | 13,272 REs | 14.22 MHz / 13.68 MHz |
| 20 MHz | 106 PRBs | 51 PRBs | 24 PRBs | N/A | 17,808 REs | 19.08 MHz / 18.36 MHz |
| 25 MHz | 133 PRBs | 65 PRBs | 31 PRBs | N/A | 22,344 REs | 23.94 MHz / 23.40 MHz |
| 30 MHz | 160 PRBs | 78 PRBs | 38 PRBs | N/A | 26,880 REs | 28.80 MHz / 28.08 MHz |
| 40 MHz | 216 PRBs | 106 PRBs | 51 PRBs | N/A | 36,288 REs | 38.88 MHz / 38.16 MHz |
| 50 MHz | 270 PRBs | 133 PRBs | 65 PRBs | 32 PRBs (FR2) | 45,360 REs | 48.60 MHz / 47.88 MHz |
| 60 MHz | N/A | 162 PRBs | 79 PRBs | N/A | 27,216 REs | 58.32 MHz / 56.88 MHz |
| 80 MHz | N/A | 217 PRBs | 107 PRBs | N/A | 36,456 REs | 78.12 MHz / 77.04 MHz |
| 100 MHz (C-Band) | N/A | 273 PRBs | 135 PRBs | 66 PRBs (FR2) | 45,864 REs | 98.28 MHz / 97.20 MHz |
| 200 MHz (FR2) | N/A | N/A | 264 PRBs | 132 PRBs | 44,352 REs | 190.08 MHz |
| 400 MHz (FR2) | N/A | N/A | N/A | 264 PRBs | 44,352 REs | 380.16 MHz |