Bhagavad Gita Chapter 8 Verse 17 भगवद् गीता अध्याय 8 श्लोक 17 सहस्रयुगपर्यन्तमहर्यद्ब्रह्मणो विदुः। रात्रिं युगसहस्रान्तां तेऽहोरात्रविदो जनाः।।8.17।। हिंदी अनुवाद - स्वामी तेजोमयानंद ।।8.17।। जो लोग ब्रह्मा जी के एक दिन की अवधि जानते हैं जो कि सहस्र वर्ष की है तथा एक सहस्र वर्ष की अवधि की एक रात्रि को जानते हैं वे दिन और रात्रि को जानने वाले पुरुष हैं।। Kumara Vaishnava Sampradaya - Commentary Those who through the power of yoga or the individual consciousness attaining communion with the ultimate consciousness understand that Brahmasday lasts for 1000 Maha Yugas. Each of which is one cycle of the four yugas or ages combined which are Satya Yuga lasting 1,728,000 Earth years, Treta Yuga lasting 1,296,000 years, Dvarapa Yuga lasting 864,000 years and Kali Yuga lasting 432,000 years all together totalling 4,320,000 years. When multiplied by 1000 Brahmas day equals 4 billion 320 million years. The same total applies also for Brahmas night. So combined one day and one night of Brahma equals 8 billion 640 million years and this is known as a kalpa. One year of Brahma equals 360 of these kalpas totalling 26 trillion, 438 billion and 400 million. Brahma lives for 100 of these years.