That's an excellent question, and it gets to the heart of creating comfortable and supportive seating. For proper ergonomics, the standard and recommended height for a bench seat from the top of the seat to the ground is typically between 17 to 19 inches (approximately 43 to 48 cm).
This range is not arbitrary. It's designed to allow the average person's feet to rest flat on the ground with their knees bent at roughly a 90-degree angle when seated. This position promotes good posture, reduces pressure on the thighs, and allows for easy standing up and sitting down.
However, the "perfect" height can vary slightly based on the bench's primary use and the user. A dining bench might be at the higher end of the range to align with a table, while a low garden contemplative bench might be lower. For universal design, 18 inches is often considered a reliable sweet spot that accommodates most adults comfortably.
Remember, ergonomics also involves depth and back support, but getting the height right is the fundamental first step to ensuring your bench is inviting and comfortable for everyone.