Strength training
O'Conner Formula: Calculate Your 1RM Simply
The O'Conner formula is direct and easy to remember, perfect for estimating 1RM without fuss.
What the O'Conner formula is and where it comes from
The O'Conner formula is one of the simplest models for estimating one-rep max. Its main appeal is simplicity: a single operation any coach can do in their head.
Because of that simplicity it has become a common choice for quick estimates in the gym, when you need a reference number without reaching for a calculator.
The formula and how to apply it step by step
The O'Conner equation is: 1RM = weight × (1 + reps / 40). It is very similar to Epley but divides by 40 instead of 30, which makes it slightly more conservative.
Worked example: a client benches 175 kg for 5 reps. 1RM = 175 × (1 + 5/40) = 175 × 1.125 = roughly 196.9 kg. For a heavy reference set, O'Conner returns about 205 kg.
The calculation is so direct that you can do it mid-session: ideal for on-the-fly adjustments when a client beats the planned reps.
When to use the O'Conner formula
O'Conner is perfect when you prioritize speed and simplicity over maximum accuracy. It works well in low and medium ranges and is a more cautious alternative to Epley.
Strength
Instant mental math and slightly more conservative results than Epley.
Limitation
Its simplicity means less fine-tuning than formulas like Brzycki in the heavy range.
Best use case
Quick gym estimates and on-the-fly adjustments on sets of 3-8 reps.
Comparison with the other four formulas
For the same heavy reference set, O'Conner returns about 205 kg, just below Epley (206.7 kg) and above Lander (202.8 kg), Brzycki and Lombardi (200 kg).
By sharing structure with Epley but dividing by 40, O'Conner offers a middle ground: a bit more cautious than Epley without being as conservative as Brzycki or Lombardi. It is a good consensus value.
How to use 1RM in your clients' programming
With the O'Conner estimate you can set load percentages quickly and reasonably, then fine-tune with RPE or RIR based on the client's response. It is practical for day-to-day gym work.
In TrainerStudio you log the estimated 1RM, generate target loads and track each client's strength progression to confirm your prescriptions work in practice.