The short answer is that you can upload up to 3 hours of audio to SoundCloud for free. This amounts to around 180 songs if each song is an average of 3 minutes long. If you have a shorter song, you can upload more per hour, and if you have a longer song, you can upload fewer.
The long answer is that there are some exceptions and caveats to this rule. For example, if your account is verified, you can upload up to 6 hours of audio. And if you're a Pro Unlimited user, you can upload an unlimited amount of audio. So, it really just depends on what level of service you're paying for.
Free users also have some other limitations imposed on them. For example, they can only upload 2GB of data per month and they can only receive 1GB of data per month from downloads (i.e., people downloading your songs). In other words, if people are downloading your songs more than they're streaming them, you'll need to upgrade your account to a paid plan in order to continue using SoundCloud To Mp3 without any hiccups.
SoundCloud is a great way to share your music with the world. The free plan allows you to upload up to 3 hours of audio, which amounts to around 180 songs. There are some exceptions and caveats to this rule, but overall it's a pretty good deal!