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UK 1RM CALCULATOR
Your Maximum Weight
Enter the weight you last trained with and the number of repetitions you completed. The calculator will estimate your 1RM using Epley’s formula.
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What is 1RM?
1RM (one-rep max) This is the maximum weight you are able to lift in a single repetition of a given exercise, whilst maintaining correct technique. It is a fundamental benchmark in strength training – it allows you to select the load precisely, rather than training „by feel”.
Knowing your 1RM comes in handy when you want to:
- plan a training cycle based on a percentage of your maximum weight,
- to gauge your strength over time without having to regularly test your true maximum,
- deliberately tailor the intensity of your training to a specific goal (strength, hypertrophy, strength endurance).
How do I use the calculator?
For the most accurate result, choose a set performed with a weight at which you completed no more than 8–10 repetitions. The more repetitions in the test set, the less precise the estimate.
1. Choose an exercise (e.g. squats, bench press, deadlift).
2. Enter the weight you used to complete the set (working weight).
3. Enter the number of repetitions completed in this set until technical failure or close to it.
4 Click "Calculate 1RM" to see your estimated maximum weight.
What is the calculator based on?
The calculator uses a tried-and-tested method commonly used in strength training Epley's manoeuvre:
1RM = weight × (1 + number of repetitions / 30)
The formula works best for sets of up to around 10 repetitions and loses accuracy for longer sets. The result is an estimate, not a guaranteed maximum value. The calculator also takes into account the selected exercise from a list of the 5 most popular strength exercises (barbell squat, deadlift, bench press, military press, bent-over barbell row) — the formula is identical for each of them; the choice of exercise only affects the description of the result.
How can you use the result in your training?
The calculated 1RM is most commonly used as a reference point for selecting the percentage range of the load:
~85–100% 1RM
– maximum strength training (low number of repetitions, longer rest periods)
~65–80% 1RM
– hypertrophy training (building muscle mass)
~50–65% 1RM
– strength-endurance training and technique
Important information for your safety:
The calculator provides only estimated values. The result is a mathematical prediction, not a guarantee of a safe weight. Your actual strength depends, amongst other things, on your technique, level of fatigue and recovery. We do not recommend attempting the calculated 1RM without proper preparation and spotter support – particularly if you are just starting strength training or returning to it after a break. The content on this website is for information and educational purposes only. Just Gym accepts no liability for training decisions made on the basis of the calculator’s estimates. If in doubt, consult a trainer.
faq
FAQs
The working weight is the load you actually train with in a given set. 1RM is the estimated maximum weight you can lift in a single attempt – calculated on the basis of the working weight and the number of repetitions.
This is an estimate. You’ll get the most accurate estimates with sets of up to 8–10 repetitions – with longer sets, the margin of error increases.
This is not necessary, and without proper preparation and safety measures, it carries a risk of injury. The calculator allows you to estimate your 1RM without having to attempt such a lift.
Every 4–8 weeks of regular strength training, or following a noticeable change in the weight you’re training with.
Yes. 1RM is calculated separately for each exercise (e.g. squats, deadlifts, bench press) – maximum strength varies depending on the muscle groups involved and the movement pattern.
No. This is a tool to help you plan your workouts – when first attempting heavier weights, it’s a good idea to use a spotter or seek support from a Just GYM trainer.