Determining the size of gobo projector you need depends on several factors:

1. **Projection Distance:** Consider the distance between the projector and the surface onto which you want to project the image. A longer projection distance typically requires a brighter projector to maintain image quality.
2. **Image Size:** Decide on the desired size of the projected image. Larger images will require more powerful projectors with higher brightness levels.
3. **Ambient Light:** Take into account the amount of ambient light in the environment where you'll be using the projector. More ambient light may require a brighter projector to maintain visibility of the projected image.

4. **Image Clarity:** Consider the level of detail and clarity you want in the projected image. Higher resolution projectors will provide clearer images, especially for intricate designs or small text.
5. **Budget:** Your budget will also play a role in determining the size and quality of the gobo projector you can afford. Generally, higher-quality projectors with greater brightness and resolution will cost more.

Consulting with a professional lighting supplier or technician can also help you determine the appropriate size and specifications of gobo projector for your specific needs and environment. They can provide personalized recommendations based on factors such as venue size, intended use, and budget constraints.