Define the lift and the set
A one-repetition maximum is specific to an exercise and its execution standard. A squat to one depth, a partial squat, and a machine movement are not interchangeable measurements. Equipment, range of motion, pauses, and assistance also matter.
An estimate is most interpretable when the recorded set reflects a challenging effort with consistent technique. A warm-up set stopped far from its limit does not provide the same information as a near-limit set.
You do not need to attempt a maximal lift merely to use a training log. Submaximal performance can be tracked directly when maximal testing is unsuitable.
Compare two common estimating formulas
For load w and repetitions r, two commonly used arithmetic models are:
Epley estimate = w × (1 + r ÷ 30)
Brzycki estimate = w × 36 ÷ (37 − r)
These are estimating conventions, not laws that apply exactly to every lifter or movement. State which equation and repetition range you use. An actual completed one-repetition lift is the recorded load itself, not a reason to inflate that load with a multi-repetition estimate.
For 100 pounds lifted for 5 repetitions, Epley gives approximately 116.7 pounds, while Brzycki gives 112.5 pounds. The disagreement is useful evidence of model uncertainty, not a reason to choose the larger result automatically.
Keep units and equipment consistent
The formulas work in pounds or kilograms as long as the entered load and reported result use the same unit. Include the bar when that is part of the load convention you are tracking.
For dumbbells, state whether the load is per hand or combined. For a machine, the displayed stack value may not equal the resistance of a free-weight movement. Do not compare the numbers as if they measured identical tasks.
A change in technique or range of motion can change performance independently of strength. Note it in the log.
Why high-repetition estimates are less decisive
The relationship between repetitions and maximum load varies with muscular endurance, exercise selection, rest, and individual characteristics. Extrapolating a long set into a precise maximal load can magnify those differences.
A calculator cannot tell how many repetitions were left in reserve or whether fatigue from earlier sets affected the result. Record those conditions alongside the weight and repetitions.
Repeated estimates from comparable sets can be more useful than a single unusually strong or weak day. Look for a trend rather than treating every decimal change as a real strength gain.
Use percentages as planning inputs, not commands
If the estimated maximum is 120 pounds, 70% is 84 pounds. That multiplication does not establish that 84 pounds is the correct working weight today. The intended repetitions, sets, fatigue, technique, available increments, and training experience still matter.
A program may deliberately use a conservative training maximum below an estimated true maximum. Keep those concepts separate so percentages are not accidentally applied to the wrong base.
Round to an available load conservatively and assess execution rather than trying to match a calculated number at any cost.
Keep testing safe and appropriate
Maximal or near-maximal lifting may be unsuitable for some people or situations. Use appropriate equipment, supervision, and safety provisions for the exercise, and obtain medical or qualified coaching guidance when relevant.
Pain, dizziness, or concerning symptoms are not signals to push through to verify a formula. Stop and seek appropriate assessment.
An estimated one-repetition maximum is an educational estimate and a logging aid. It does not certify readiness for a maximum attempt, prescribe a training program, or replace observation of the actual movement.
Frequently asked questions
Is the higher of the two estimates my real maximum?
No. The formulas are models with different assumptions. Neither establishes the actual maximum, and choosing the higher value does not make it more accurate.
Can I compare a machine estimate with a barbell estimate?
Not as equivalent measurements. Equipment mechanics and movement standards differ. Track each exercise consistently on its own terms.
Should I attempt the predicted weight immediately?
The estimate is not a recommendation to attempt that load. Readiness, technique, fatigue, equipment, and appropriate supervision must be considered.
Sources & calculation notes
The formulas and worked examples above show the calculation method. All example inputs are illustrative; a mathematical result does not validate the assumptions or replace a project-specific assessment.
Use this guide thoughtfully. Educational information, not a diagnosis or individualized medical advice. A screening result or formula cannot establish what is safe or appropriate for a particular person. Consult a qualified healthcare professional for clinical decisions.