A fixed rate loan will let you know exactly what your loan repayments will be through the life of their loan. The amount that you will be able to borrow will depend on your personal incomings and outgoings (i.e. how much you have spare each month to use to repay a loan) since there is no industry average for borrowings on fixed rate loans.
You could borrow a small amount, as low as a few hundred pounds right up to £100,000+ but understand that the amounts will vary from lender to lender. Whether or not your loan is secured or unsecured will play a part as to which type of loan you will take out. The period of the loan will vary from 1 to 25 years, depending on your lender and the type of loan you want and how much you need to borrow.
You can also budget accurately because with a fixed rate loan, you will know exactly how much you payment will be each and every month throughout the life of the loan. If the interest rates rise to become higher than your rate, you will save money since your rate with always stay the same.