The results issued by Business in the Community (BITC) scored the level of publicly available information provided by organisations across 25 employee engagement and wellbeing indicators.
They highlight both the information currently available for investors to analyse how FTSE 100 organisations manage their 6.3 million employees and the need for increased transparency to show whether robust people practices are in place to drive long term success.
While the average score for all the FTSE 100 organisations was 21%, there was clear leadership from British Land Company, BT, Johnson Matthey and RBS who achieved significantly higher scores.
Stephen Howard, BITC chief executive, said: "The Workwell benchmark represents a new chapter for CSR reporting and the low average scores are not unexpected at this first stage of development.
"We are encouraged by the examples of leadership highlighted through this process, and by the commitment shown by a third of FTSE 100 companies, who proactively took part in the survey.
"We introduced our corporate responsibility index 10 years ago and have seen how organisations have built their confidence in reporting key environmental and societal benefits through sustainability reports. Now we are encouraging organisations to use data effectively to demonstrate responsible people management and drive business performance improvements."
Irwin Lee, managing director of Procter and Gamble UK and chair of the Workwell Leadership Group, said: "This is a critical first step towards open reporting on employee engagement and wellbeing, and comes at a really important time.
"Now more than ever our businesses need to demonstrate their resilience and this means people must be at the centre of both business and organisational strategy. We expect to see significant benefits for individuals and our overall businesses from this important work to consolidate and formalise public reporting of wellbeing and engagement levels in our organisations."