To work out a roughly how many hours and days will you actually be working as a contractor, ie invoiceable hours per year.
A non leap year consist of 365 days across 52 weeks. Take away weekends and you have a maximum of 260 days to invoice.
You need some holidays and you may be sick. You may want to take time off for training and conferences. You may have gaps between contracts. You will need time for administration and sales/interviews.
The US average for permanent employees are closer to 2000 hours per year, the OECD average is around 1750, while in Norway it is around 1400 hours.