Return on investment (RoI) is similar to ROCE but is a broader term that can be applied to particular projects or operations, whereas as ROCE refers to returns at the company level.
RoI is the profit an investment generates as a proportion of the value of the assets used to generate it:
EBIT ÷ value of assets
RoI obviously needs to be compared to cost of capital, but the cost of capital for a particular project may not be the same as that for a company as a whole. If an investment is in line with a company's business as a whole (in terms of risks to cash flows it will generate) then the company's cost of capital may be used, otherwise it needs to be adjusted.
One way of calculating an appropriate cost of capital for a particular investment is to use CAPM and to estimate its beta. This is often by comparison with listed companies in the same business.
Because RoI uses accounting numbers it reflects accounting conventions in the measurement of profits and the value of assets. For this reason it is often preferable to instead use ROIC or CROIC.