Strength Calculator

RIR = reps in reserve: how many more full repetitions you believe you could perform at the end of a set with the same technique. RPE is another way to describe that effort.

For example, 5 reps at 2 RIR means finish five reps feeling you could have completed roughly two more. Zero RIR means no further full rep available; you don’t need to attempt and fail another rep.

This calculator uses whole-number effort ratings from 0–4 RIR / RPE 6–10. Sets with more than 4 reps left are not suitable inputs for its 1RM estimate.

1. Warm up progressively. Treat the suggested load as a starting point for your lift.
2. Check the actual effort. If you have fewer reps left than intended, reduce the load. If you have more left, increase by a small available increment.
3. Reassess each set. Sleep, recent training, rest periods and fatigue can change what a weight feels like. Update your estimate as your strength changes.

Use the same lift, equipment, range of motion and technique for the input set and planned set. These estimates are for standard strength lifts; they don’t transfer directly to Olympic lifts, weighted pull-ups or assisted exercises.

We use the Brzycki equation and a practical RIR adjustment: potential reps = completed reps + reps in reserve. Adding RIR is a coaching approximation, not an individually validated strength test.

The percentage view uses the inverse of the same equation, so all three tools agree before display and equipment rounding. A single rep at 0 RIR returns the entered load as the 1RM.

Most useful at 10 potential reps or fewer. Results from 11–15 potential reps are rough extrapolations and are flagged. Beyond 15, precise estimates are withheld. These limits are software choices, not guarantees of accuracy within them.

Repetition capacity differs between lifters and exercises. This calculator uses a general model. Enter a separate set or known 1RM for each exercise you want to calculate. An estimated 1RM is a training reference, not a recommendation to attempt that weight.

The bar guide rounds the working load down to the nearest achievable total using your selected bar and available matching plate pairs. Set missing plate sizes to 0, or limit how many pairs are available. A pair of 1.25 kg plates adds 2.5 kg in total. The closest available load can be lower if your setup has larger gaps. With “No bar” selected, the calculated load is shown without equipment rounding. If the target is lighter than the selected bar, we keep the calculated target and flag that the bar cannot make that load. The copied set uses the same load as the result. The percentage explorer instead rounds to the nearest 2.5 kg (halfway values round up), and shows both loads. The percentage explorer keeps its fixed 2.5 kg rounding regardless of the equipment menu on Find a load. Its rep estimates use the selected percentage before rounding. In lb mode, practical loads are converted from the same kg weights. Displayed figures are simplified.

Background: Brzycki (1993) · Zourdos et al. (2016) · Nuzzo et al. (2024)