According to SIA’s biannual research, contingent work in the US accounted for $864 billion in 2017. Broken down by worker source, an 8.8% increase from the prior research conducted in 2015, or 4.3% on an annualized basis. Independent contractors/self-employed workers with no employees (excluding 1099/self-employed workers already reported as temporary agency or human cloud workers) accounted for nearly half the spend, at $426 billion, while statement-of-work contractors through consulting firms came was second, at $246 billion. The human cloud category, which earlier this month saw the successful IPO of Upwork, accounted for a slim slice of the market at $24 billion. Meanwhile, US businesses spent $246 billion on temporary workers sourced through staffing firms, and $43 billion on self-sourced temporary workers.
Source: The US Gig Economy, 2018 Edition  report
* Numbers do not add up due to rounding.