RPE Calculator: Work Out Today's Training Weights

How to use it

1. Choose kilograms or pounds.
2. Enter a working set you did recently and remember clearly: the weight and the reps you completed.
3. Enter the RPE that set felt like. RPE 8 means you had two reps left, RPE 9 means one, RPE 10 means none.
4. Enter the RPE you want to train at today.

The calculator returns a weight for every rep count from 1 to 10 at that target RPE, and the estimated one-rep max it derived them from.

If you leave the target RPE the same as your reference set's, your own weight appears in the table at your own rep count. That is the arithmetic checking itself, and it is worth glancing at before you trust the other rows.

What this calculator does that the other one does not

Lift has two RPE tools, and they run the same relationship in opposite directions.

• This one is forward-looking. You know what you lifted last time; you want to know what to put on the bar today. Reference set in, prescribed weights out.
• The RPE to percentage calculator is backward-looking. You know what you lifted; you want to know what it was worth as a percentage of your max. One set in, one percentage out.

Same formula, opposite questions. Use this one when you are about to train, and that one when you are reviewing a session or reading a program written in percentages.

What the inputs and outputs mean

Reps plus the reps you had left cannot exceed 12, and rows are dropped from the table when they would put you more than 12 reps from failure. Both limits exist for the same reason: past roughly a dozen reps to failure the equation stops being dependable, and a number the tool cannot stand behind is worse than no number.

RPE is taken in whole numbers from 6 to 10. Half points are common in programs, but they are a convention rather than a research finding, and given how imprecise effort estimates are, a half-point of RPE is well inside the noise. If you are unsure which number your set was, the RPE scale describes each one and when it belongs in your training.

The formula

Everything rests on one idea: a set of 5 with 2 reps left is the same effort as a set of 7 taken to failure. So the first step converts effort into reps.

reps to failure = reps completed + (10 - RPE)

Your reference set then gives an estimated max through the Brzycki equation, the same one the one-rep max calculator uses:

estimated 1RM = weight / (1.0278 - 0.0278 x reps to failure)

And each target weight runs the equation backwards from that max:

target reps to failure = target reps + (10 - target RPE) weight = estimated 1RM x (1.0278 - 0.0278 x target reps to failure)

The estimated max is carried at full precision through that second step and rounded once at the end, so repeated conversions do not accumulate rounding drift.

Worked example

Say you squatted 100 kg for 5 reps and it felt like RPE 8.

Reps to failure is 5 + (10 - 8) = 7, so the estimated max is 100 / (1.0278 - 0.0278 x 7) = 120.0 kg.

Ask for RPE 8 work and you get:

Five reps comes back at 100 kg, which is exactly the set you entered. Ask for RPE 7 instead and every weight drops by about one rep's worth, roughly 2.8 percentage points of your max.

Assumptions and limitations

• The output is only as good as your RPE call. Research pooling a dozen studies found people underestimate what they have left by about one rep on average, and that the estimate does not improve with training experience. One rep is roughly 2.8 percentage points here, so a misjudged RPE moves every weight in the table.
• It is one formula's estimate, not a measured max. Different equations disagree about the same set. The one-rep max calculator offers three and they return different numbers.
• It assumes one exercise. An estimate from your squat says nothing useful about your lateral raises. Run it per lift.
• It assumes consistent technique and range of motion. A rep you would not count is not a rep the formula should count either.
• Long sets are the weakest case. Both the equation and your own judgment are least reliable above about 10 reps to failure, which is why the table stops where it does.
• It cannot tell you whether a weight is appropriate or safe for you. If something hurts, or an injury or medical condition could change the answer, ask a qualified professional rather than a calculator.

What to do with the numbers

Treat each weight as the middle of a range rather than a prescription. If your reference set was a genuine RPE 8, the honest reading of a prescribed weight is a couple of percent either side of what the table says.

Then round to what you can actually load. The weight plate calculator works out whether 93.3 kg is something your bar and plates can make, which it usually is not; 92.5 kg is close enough and it is the difference between a plan and a plan you can execute.

Let the set have the final say. If the prescribed weight comes in at RPE 6, the estimate was low and the next one goes up. That is not the calculator failing, it is the calculator doing its job: giving you a defensible starting point so the session decides the rest.

Recording effort, not just weight

The estimate above is only as current as the set you fed it. A reference set from two months ago describes the lifter you were two months ago.

Lift stores an RPE value alongside weight and reps on every set, shows last session's numbers on the set you are about to log, and keeps an estimated one-rep max across your whole history, so the reference set is always your most recent one rather than the one you happen to remember. Automatic progression can raise the load for you once a set comes in easy, and is part of Lift Premium with a 2-week free trial. See how the Lift app handles progressive overload, or read how to measure training intensity for what RPE does and does not tell you.