One billion seconds equals approximately 31.7 years. To calculate: one minute has 60 seconds, one hour has 3,600 seconds, and one day has 86,400 seconds. Dividing one billion (1,000,000,000) by 86,400 gives about 11,574 days. Dividing that by 365 results in roughly 31.7 years, making one billion seconds just over three decades long.