Credit utilization measures how much you're spending of your available credit limit from all cards combined.
For example, let's assume you have three different credit cards, with individual credit limits of $1,000, $4,000 and $5,000. Your total available credit will be the sum of these credit limits: $10,000.
Let's also say your current balances on these three cards are $350, $500, and $150. Your total outstanding balance is the sum of these: $1,000.