Lapping of reinforcement is usually done where minimum bending stress is required. In general, lap length is 50d which means 50 times the bar diameter is provided if both bars are of same diameter.

Lap length in tension:
The lap length including anchorage value of hooks shall be

For flexural tension – Ld or 30d whichever is greater is considered.
For direct tension – 2Ld or 30d whichever is greater is considered.
The straight length of lapping of bars shall not be less than 15d or 20cm.

Lap Length in Compression:
The lap length is equal to the development length calculated in compression but not less than 24d.

For Different Diameter Bars:
When the bars of different diameters are to be spliced, the lap length is calculated considering the smaller diameter bar.