Technically, the value of formed capital should be equal to its present value of the contribution of capital to future revenue flows. This might be hard to estimate.
It will be tempting to use the cost of the project as a proxy for its capital value, but the cost might include a lot of R&D and experimentation/errors/learning etc.
You can say how much the project cost, and the number of people who can do what in which different ways, compared to what they could have done without access to that capital.
This is one of the reasons that it is difficult to defend public sector activities compared to the private markets. Even when they provide services or create capital that is absolutely critical to a functioning economy, the fact that it is difficult to evaluate compared to the financing/accounting of private sector projects makes it very difficult to say that it was "efficient" per se.