How this works
The estimate uses the Epley formula, which multiplies the weight by one plus the reps divided by thirty. It is most accurate for sets of about 3 to 10 reps and gets less reliable as reps go up.
The percentage table shows rough weights for training at different intensities. The rep numbers are typical, and people vary a lot. Use it to pick starting weights, then adjust by feel.
You do not need to test a true one-rep max. Heavy singles carry more risk, so use a spotter or safety bars if you ever try one, and work up to it gradually. For beginners, a set of 5 to 10 clean reps tells you what you need to know.