The Capital One Platinum credit limit is $300 or more, depending on your creditworthiness. So as long as you're approved for the card, you're guaranteed at least a $300 spending limit. But if your credit score and income exceed what Capital One is looking for, you could definitely start off with a higher limit. Some users have reported Capital One Platinum credit limits of $500 to $1,500 to start.

Keep in mind that you aren't stuck with your starting Capital One Platinum credit limit forever. Capital One may increase your limit if you make your first 5 payments on time. You can also request an increase yourself. Many users report their limits increasing over time.

Capital One Platinum credit limit details:

You're guaranteed a credit limit of at least $300 if you're approved for Capital One Platinum.
Capital One Platinum only requires limited credit for approval. If you have good credit or a lot of income relative to your debt, you'll likely start with a higher limit. Some users report getting $500-$1,500 initially.
Capital One may increase your credit limit after you make your first 5 monthly payments on time. After the first 5 months, they will review your account periodically to see if you deserve a higher limit. Pay more than the minimum each month, if possible, to boost your chances.
You can request a credit limit increase yourself by calling customer service at 1 (800) 227-4825. You can also log into your Capital One account. Just choose “Request Credit Line Increase” from the “Services” tab. You'll have to provide information about your income and employment for Capital One to make their decision.

So you'll get $300+ from Capital One Platinum to start. If you use your card responsibly, you'll provide yourself with opportunities to increase your limit. But it's best not to ask for an increase before five months of on-time payments, as you'll probably be denied. If you do request an increase, Capital One may generate a hard inquiry, or “hard pull,” of your credit report. This will cause a slight drop in your credit score. That's pretty standard.