If you use one of the popular webmail services, odds are you have a few gigabytes of online storage included for storing your messages, photos and documents. But the longer you have the account, the more you’re likely to fill it up. Then you either have to delete stuff — or whip put the plastic and pay money for more storage space from the provider.

Unless you’ve gotten warnings about running out of room, you may not have had to check your current storage situation. But do you know what types of files actually count towards your storage total — or ways some sites give you way to earn free additional storage? Read on.

First off, Yahoo Mail users: You get a get a free terabyte of space for your mail. So unless you’re running an enormous mailing list or have a digital hoarding problem, you’re going to be okay for awhile.

If you use Google products to store your life online — Gmail, Google Drive and Google+ Photos — you get 15 gigabytes for free to divide up between the three services. Your Gmail attachments count toward this limit, as well as the files you’ve stored on your Google Drive — unless those files are Google Docs, Sheets or Slides files. Files that have been shared with you also don’t count, and neither do photos smaller than 2048 x 2048 pixels and videos longer than 15 minutes. (Brevity is the soul of wit, and it has other perks, too.)

If you think you may be getting close, check your Google Storage page to see how your 15 gigs are carved up between the services you use regularly. Google occasionally offers a free gigabyte or two, as it recently did for users who completely a security checklist on their Google accounts, so keep an eye out for those types of things. But if space gets tight, an extra 100 gigabytes is about $2 a month, a terabyte is $10 a month — and you can even get more if you need it.

Microsoft OneDrive also provides 15 gigabytes of free storage when you sign up for an account or use it with your Outlook.com mail or other Microsoft service. As a perk, you also get to use Office Online. As an even bigger perk, Microsoft will double your overall storage locker and give you another 15 gigabytes of space if you use the OneDrive app on your iPhone, Android phone or Windows Phone to automatically back up the photos you take on the mobile device. You can get another 500 megabytes of space if you refer a friend to OneDrive — and the friend gets 500 megabytes, too. (You can refer up to 10 of your pals, which gives you a max of 5 extra gigs you can add on through referrals.) Still need more? Microsoft has plans: 100 gigabytes for $2 a month, 200 gigabytes for $4 a month or a whole terabyte for $7 a month — and you get Office 365 with that big TB.

In comparison, Apple’s iCloud is quite stingy, perhaps in the hope that you’ll fork over some bucks to upgrade your space. The five starter gigabytes are divided up between your iCloud mail, online backup, iCloud Drive and iCloud Photo Library.

Need more? To get a total of 20 gigs, you pay Apple a buck a month. And there are other plans — a total of 200 gigabytes costs $4 a month, 500 gigs is $10 monthly and a terabyte is $20 a month. If you buy a lot of content from iTunes, though, you don’t have to worry about those purchases eating up your space — all those items don’t count toward your iCloud total.

And last but not least. Dropbox starts you off with two gigabytes with your free account, but gives you all kinds of ways to add extra space to your storage total. If you use the company’s new photo gallery mobile app, Carousel, you get an extra 3 gigabytes of space. You can also earn extra storage space for linking Dropbox with its Mailbox app, referring your friends, sending feedback to the company, connecting your Dropbox to your Facebook and Twitter accounts and following the company on Twitter. If fact, Dropbox has a whole Get More Space page you can visit to learn all the ways you can add on to those original two gigs if you start running low. And if you still need more, you can always upgrade to Dropbox Pro, which starts you out at a terabyte of storage space for $10 a month.

To keep up with demand, these companies seem to be adding server racks left and right to store the bits and bytes of the world. In that regard, it seems like this sort of space isn’t the final frontier after all.