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In short
An estimated 1RM turns a set into a max without testing a single.
With RPE, the reps you had left count as reps done.
Track the trend over weeks. One high number changes nothing.
Start with a set you already did
How SBD Guru works it out
SBD Guru uses the Epley method to turn the weight, reps and RPE of a set into an estimated max. With no RPE, only the reps you did count. With RPE, the reps you had left count as reps done. A single at RPE 10 is the weight you lifted. The 1RM calculator also asks which lift the set was. Squat and deadlift sets read a little lower than bench sets, by up to 4 percent. Lifters get more reps from those two lifts at the same share of their max.
An example
100 kg for 5 with no RPE comes out at 116.7 kg. Rate the same set RPE 8, and the two reps you had left count too. The estimate rises to 123.3 kg.
The second number is higher because you said you had more left. You did not get stronger.
Know the limits
Rep estimates can be off. A study of bench press and leg press found accuracy changed with the rep test used. Counting the reps you had left is a simple rule, not a measured one. With ten reps at RPE 5, the estimate has to guess far beyond the set you did.
Use the trend
Compare estimates from similar rep ranges, effort and variations. A paused bench and a touch-and-go bench need separate lines. A steady rise tells you the block is working. One high estimate should not reset your loads or pick your meet attempts.