Of the two approaches in this guide, this one is easier for most people to follow. If you're already comfortable with different bases, try the faster method below. If you're completely new to hexadecimal, you might want to learn the basic concepts. Each digit in a hexadecimal number represents a different power of 16, just like each decimal digit represents a power of 10. This list of powers of 16 will come in handy during the conversion:  165 = 1,048,576 164 = 65,536 163 = 4,096 162 = 256 161 = 16 If the decimal number you're converting is larger than 1,048,576, calculate higher powers of 16 and add them to the list. Write down the decimal number you're about to convert. Refer to the list above. Find the largest power of 16 that's smaller than the decimal number. For example, if you're converting 495 to hexadecimal, you would choose 256 from the list above. Stop at the whole number, ignoring any part of the answer past the decimal point.  In our example, 495 ÷ 256 = 1.93... , but we only care about the whole number 1. Your answer is the first digit of the hexadecimal number. In this case, since we divided by 256, the 1 is in the "256s place." This tells you what's left of the decimal number to be converted. Here's how to calculate it, just as you would in long division:  Multiply your last answer by the divisor. In our example, 1 x 256 = 256. (In other words, the 1 in our hexadecimal number represents 256 in base 10). Subtract your answer from the dividend. 495 - 256 = 239. Refer back to your list of powers of 16. Move down to the next smallest power of 16. Divide the remainder by that value to find the next digit of your hexadecimal number. (If the remainder is smaller than this number, the next digit is 0.)  239 ÷ 16 = 14. Once again, we ignore anything past the decimal point. This is the second digit of our hexadecimal number, in the "16s place." Any number from 0 to 15 can be represented by a single hexadecimal digit. We will convert to the correct notation at the end of this method. As before, multiply...

TL;DR in Vietnamese:
Dùng phương pháp này nếu bạn chỉ mới làm quen với hệ thập lục phân. Viết xuống lũy thừa của 16. Tìm lũy thừa lớn nhất của 16 phù hợp với số thập phân của bạn. Chia số thập phân cho giá trị lũy thừa vừa chọn được. Tìm số dư. Lấy hiệu vừa thu được chia cho lũy thừa cao nhất tiếp theo của 16. Tiếp tục tìm số dư. Lặp lại cho đến khi số dư nhỏ hơn 16. Biểu diễn đáp án theo ký pháp thập lục phân. Kiểm tra lại.