How to Calculate Your 1RM, Step by Step

Published 25 October 2026 · 8 min read

You do not need to grind out a risky single to find your one-rep max. A hard set at a moderate rep count, a formula, and five minutes of arithmetic will get you an estimate good enough to program with. This guide walks through the whole process: choosing the set, running the numbers, checking that they make sense, and converting the result into actual training weights.

What you need before you calculate

One honest, hard set with clean technique. That is the entire input. The quality of your estimate is decided the moment you rack the bar — no formula can rescue a set that ended five reps short of failure, or one where depth got shabby on rep four.

Three rules make a set usable:

• Five reps or fewer is the sweet spot. Estimates stay reasonably dependable to eight or ten, but accuracy falls as reps rise.
• The set should be near-limit — you could maybe have forced out one more rep, not four.
• Same exercise, same standards every time. A high-bar squat to depth and a low-bar squat to a box are different numbers.

Step 1: choose your working set

Pick a weight you are confident you can handle for a small number of solid reps. A common approach is to work up to something around your three-to-five rep best for the day. Warm up thoroughly with progressively heavier, lower-rep sets first, and take two to three minutes of rest before the working attempt so fatigue does not bias the result.

Record exactly what happened: the weight on the bar, the reps you completed, and the exercise variation. If you lifted 102.5 kg for 5 because that is how the plates fell, use 102.5 — do not round before calculating.

Step 2: pick a formula

The two most established options are Epley (1985) and Brzycki (1993):

• Epley: 1RM = weight × (1 + reps ÷ 30)
• Brzycki: 1RM = weight × 36 ÷ (37 − reps)

Both are well validated at low rep counts, and our Epley vs Brzycki comparison shows exactly where they agree and disagree. If you want a single default, Epley is the most widely used; averaging the two is also a defensible choice.

Step 3: work the numbers

Example: you squatted 100 kg for 5 reps.

• Epley: 100 × (1 + 5⁄30) = 100 × 1.1667 = 116.7 kg
• Brzycki: 100 × 36⁄(37 − 5) = 100 × 1.125 = 112.5 kg

Your estimated 1RM sits around 113–117 kg. Run the same set through the calculator and you will see the full spread of the seven supported formulas — Lombardi, O'Conner, Wathan, and Lander land between roughly 112 and 120 kg for this input.

Step 4: sanity-check the result

Estimates are only useful if they pass the smell test. Two quick checks:

• Rep-max percentages. A five-rep set should estimate a 1RM you could roughly lift for a double. Standard percentage charts put a 5RM near 85–87% of 1RM; 100 ÷ 0.86 ≈ 116 kg, which matches the formulas above. If your math says something wildly different, re-check the inputs.
• Training history. If you have previously squatted 120 kg for a single and today's estimate says 150 kg, be suspicious of the set — it was probably shallower or faster than you remember, or the rep count was generous.

Step 5: turn the estimate into training weights

This is the whole point of the exercise. Programs prescribe loads as percentages of 1RM, so multiply your estimate by the target intensities:

Round each to the nearest loadable increment, then adjust by feel in the first session. If 80% moves crisply, the estimate was fair; if it grinds, work a notch lighter until form and speed return.

Common mistakes that skew estimates

Using high-rep sets

A twenty-rep set tells you about conditioning and pain tolerance, not maximum strength. Every extra rep compounds the formula's assumptions; keep estimate inputs at five reps or fewer whenever possible.

Counting loose reps

If the last reps lost range of motion or bar speed collapsed, the set was over before you racked it. Count the clean reps only — an estimate built on six honest reps beats one built on nine sloppy ones.

Mixing exercise variations

Your paused bench and touch-and-go bench are different lifts with different maxes. Track them separately, and calculate from the variation you actually program.

Recalculating too often

Daily estimates bounce around with fatigue and sleep. Re-estimate every few weeks, or watch the trend in your Training Tracker instead of chasing single-session numbers.

Common questions

Can I calculate a 1RM from a 3-rep max?

Yes — three reps is an excellent input. Epley gives weight × 1.1 and Brzycki gives weight × 1.091 for a triple, so the two agree within a percent. Triples are arguably the best balance of load and safety for estimation.

Do these formulas work for dumbbells and machines?

The arithmetic runs fine on any load-and-reps input, but the classic equations were validated on barbell lifts. Dumbbell and machine estimates are rougher; use them for tracking trends on the same station rather than as absolute numbers.

Should I just test my real 1RM instead?

Testing gives you the true number, with more fatigue and more risk. If you want a tested max, follow a proper protocol — see our safe 1RM testing guide. For programming purposes, an estimate from a hard set of three to five is usually all you need.

Conclusion: estimate, sanity-check, program

Calculating your 1RM is a five-step loop: take one honest set of five reps or fewer, run it through a formula, check the result against percentage charts and your training history, convert it into working weights, and repeat every few weeks. Do that consistently and the estimate becomes a reliable steering wheel for every percentage-based program you run.

Related articles

• Epley vs Brzycki: Which Formula?

  Where the two classic formulas agree, and where they drift apart.

• How to Test Your 1RM Safely

  A full warm-up and attempt protocol for when you want a tested max.

• What Is 1RM?

  The definition, and what the number does and does not tell you.