Tools / nr-tbs-calculator

5G NR Transport Block Size Calculator

Calculate 5G NR transport block size for both downlink and uplink using the latest 3GPP NR TBS procedure from TS 38.214 Release 18.

Transport Block Inputs

Direction

MCS Table

MCS Index

Layers per TB

Allocated PRBs

Allocated Symbols

DM-RS RE / PRB

xOverhead (RE / PRB)

TB Scaling

Selected Modulation -

Target Code Rate -

MCS Table Note -

Adjust the parameters and calculate.

Transport Block Size -

Branch -

Total Allocated REs -

Ninfo -

Field	Value
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Select Downlink for PDSCH or Uplink for PUSCH.
Choose the applicable MCS table and MCS index. The tool will show the resulting modulation order and target code rate.
Enter the scheduled PRBs, number of allocated symbols, and the total DM-RS RE per PRB.
Set xOverhead if the configuration uses one of the standardized overhead values.
For UL, enable transform precoding if needed. For the transform-precoded low-index cases, you can also enable pi/2-BPSK.
Use TB Scaling only for the downlink RNTI cases that apply transport block scaling; otherwise keep it at 1.
Press Calculate TBS and review the result and intermediate values.

Specification basis: TBS determination follows TS 38.214 Release 18 clause 5.1.3.2 for DL and clause 6.1.4.2 for UL.
RE cap: total RE uses min(156, NRE') per PRB, as specified.
Small TBS branch: when Ninfo ≤ 3824, the calculator uses the standardized TBS lookup table.
Large TBS branch: when Ninfo > 3824, the calculator uses the quantization and code-block-aware rounding defined in the spec.
Per-TB scope: this calculator computes one transport block. For dual-codeword scheduling, calculate each codeword transport block with its own parameters.
UL tables: transform-precoded PUSCH uses the dedicated UL MCS tables, including the pi/2-BPSK-dependent low-index rows.