One of the first formulas you'll learn in high-school physics is that distance travelled (D) equals speed (s) multiplied by time travelled (t), or:
D = s * tSo if you're going 30 km/h for 3 hours, you know you've travelled 90 kilometers.
The same formula can be applied to language learning, where learning (D) equals learning speed (s) multiplied by time spent learning (t). So if you've been learning 1 new item (vocab word, grammar rule, character, etc.) every 3 minutes and your exposure time is 100 hours (or 6,000 minutes), you've learned 2,000 items.