The number of sparklers you will need for 100 guests depends on a few factors, such as how many sparklers each guest will use and how long you want the send-off to last. Here's a general guideline:

1. Determine the number of sparklers per guest: On average, one sparkler per guest is usually sufficient. However, if you want to create a more dazzling effect or have a longer send-off, you might consider providing each guest with two sparklers.

2. Estimate the burn time: Consider the burn time of the sparklers you have chosen. For example, if you have 36-inch sparklers with a burn time of approximately 4 minutes, you can calculate how many sparklers you'll need based on the desired send-off duration.

3. Calculate the total number of sparklers: Multiply the number of sparklers per guest by the number of guests. For instance, if you plan to give each guest one sparkler, you will need 100 sparklers. If you choose to provide two sparklers per guest, you will need 200 sparklers.

4. Consider extra sparklers: It's a good idea to have a few extra sparklers on hand in case of any issues with lighting or if guests want additional sparklers. Adding around 10% to your total number of sparklers should account for any extras you might need.

Remember to consult with your venue regarding any restrictions or guidelines on the use of sparklers. Additionally, check local regulations and safety guidelines to ensure a safe and enjoyable experience for everyone involved.

By estimating the number of sparklers needed based on the number of guests and your desired send-off duration, you can ensure that you have enough sparklers to create a beautiful and memorable wedding send-off.