The exchange rate between the US dollar (USD) and the Nigerian naira (NGN) is constantly fluctuating. To determine how much a 100 USD Amazon gift card is worth in naira, one has to check the current exchange rate.

Exchange rates are influenced by various factors such as economic conditions, central bank policies, and market sentiment. Financial institutions offer different rates for currency exchanges. It's essential to look for a reliable source to get an accurate rate.

When converting, multiply the amount in USD (in this case, 100) by the current exchange rate. For example, if the exchange rate is 1 USD = 410 NGN, then 100 USD would be 100 * 410 = 41,000 NGN. However, this amount can change depending on when the conversion occurs.