One Rep Max (1RM) Calculator

What is a one-rep max (1RM)?

Your one-rep max is the heaviest weight you can lift for a single, full repetition of an exercise with correct form. It is the standard benchmark for strength and the reference point most training programs use to set day-to-day loads. Because grinding out a true single is fatiguing and risky, this calculator estimates your 1RM from a lighter set — the weight and the number of reps you performed — using two well-established equations.

How do you estimate a one-rep max?

You estimate 1RM by feeding a submaximal set into a prediction formula. This calculator uses the two most common ones:

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

Enter the weight and reps, and the tool returns the Epley estimate as the headline number plus the Brzycki estimate for comparison. It then builds a percentage-of-1RM table so you can turn that single number into loads for every rep range.

Worked example 1: 100 kg for 5 reps

• Epley: 100 × (1 + 5/30) = 100 × 1.1667 = 116.7 kg
• Brzycki: 100 × 36 / (37 − 5) = 100 × 36/32 = 112.5 kg

So a clean set of 5 at 100 kg suggests a max of roughly 113–117 kg. The two formulas bracket the likely truth, and the spread of about 4 kg is the natural uncertainty you should expect.

Worked example 2: 60 kg for 8 reps

• Epley: 60 × (1 + 8/30) = 60 × 1.2667 = 76.0 kg
• Brzycki: 60 × 36 / (37 − 8) = 60 × 36/29 = 74.5 kg

Here the estimates sit close together at about 75–76 kg. Notice that at 8 reps Epley is the higher of the two — that gap widens as reps increase.

What is a %1RM training-load table?

A %1RM table converts your estimated max into the working weights you actually load on the bar, matched to a rough rep target. The values below come from a 117 kg estimated max (the Epley result from example 1), computed exactly as the calculator does — by applying each percentage to the unrounded estimate and rounding the result:

% of 1RM	Weight (≈117 kg max)	Approx. reps	Typical use
100%	117 kg	1	Max / test single
95%	111 kg	2	Heavy strength
90%	105 kg	4	Strength
85%	99 kg	6	Strength–hypertrophy
80%	93 kg	8	Hypertrophy
75%	88 kg	10	Hypertrophy / volume
70%	82 kg	12	Volume / endurance

To read your own numbers, run the calculator with your lift and reps — the live table recalculates every weight automatically. As a quick rule of thumb, each ~5% drop in load buys you roughly two extra reps.

How accurate is an estimated 1RM by rep range?

Accuracy is highest from low-rep sets and degrades as reps climb. Below about 10 reps the estimate is usually within a few percent of a tested max; beyond that, the result depends heavily on muscular endurance and is best treated as a ballpark.

Reps used	Accuracy	Notes
1–3	Excellent	Minimal extrapolation; trust the number
4–6	Very good	The sweet spot for most strength testing
7–10	Good	Reliable for programming, slightly conditioning-dependent
11–12	Fair	Wider error band; use as a rough guide only

This is why the input is capped at 12 reps. A hard set of 2–5 reps taken close to failure gives the most dependable estimate for the least fatigue.

How do you use 1RM for programming?

Use your estimated max as the anchor for every working set, then assign percentages to match each session’s goal. A simple weekly split might be heavy strength work at 85–90% (4–6 reps), a hypertrophy day at 75–80% (8–10 reps), and lighter technique volume at 70%. Programs such as 5/3/1 deliberately base their numbers on about 90% of your true max — a “training max” — to leave a safety margin and keep the bar speed fast.

Practical tips:

• Round to the plates you own. A 93 kg target becomes 92.5 kg or 95 kg in the real world — close enough.
• Re-estimate every 4–8 weeks rather than chasing a new max each session.
• Track each lift separately. Your bench, squat and deadlift maxes progress at different rates.
• Warm up to your top set. A single all-out set off cold muscles both under-reads and raises injury risk.

For broader number-crunching you can pair this with our percentage calculator to adjust loads, or browse more training tools in the fitness category. If you are also tracking body composition, the BMI calculator is a useful companion.

Common mistakes and limitations

The biggest error is using a set you did not take near failure — leaving three reps in the tank quietly under-predicts your max. Other pitfalls:

• Mixing units. Decide on kg or lb and keep weight and bar loading consistent.
• Over-testing. Frequent max attempts add fatigue without sharpening your programming numbers.
• Trusting high-rep sets. A 20-rep effort is a cardio test as much as a strength test; the formulas were never built for it.

Accuracy note: all 1RM equations are population averages. Your personal “rep strength” — how many reps you can grind at a given percentage — varies with the exercise, your training history and fibre type. Expect the estimate to land within a few percent, not to the kilogram.

Safety disclaimer: this calculator is for general fitness and educational purposes only and is not medical advice. Heavy and maximal lifting carries injury risk. Warm up thoroughly, use proper technique and a spotter where appropriate, and consult a qualified coach or physician before starting or changing a resistance-training program.