Strength Calculator

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Strength & One-Rep Max Calculator
One-Rep Max (1RM)Strength-to-Weight RatioWilks Score (Relative Strength)
MaleFemale
Result:

One-Rep Max = 0.00
function updateFields(){var type=document.getElementById('calc_type').value;var rowReps=document.getElementById('row_reps');var rowGender=document.getElementById('row_gender');if(type==='1rm'){rowReps.style.display='table-row';rowGender.style.display='none';}else if(type==='ratio'){rowReps.style.display='none';rowGender.style.display='none';}else if(type==='wilks'){rowReps.style.display='none';rowGender.style.display='table-row';}}function calculateStrength(){var type=document.getElementById('calc_type').value;var w=parseFloat(document.getElementById('input_weight').value);var r=parseFloat(document.getElementById('input_reps').value);var bw=parseFloat(document.getElementById('input_bw').value);var gen=document.getElementById('input_gender').value;var showSteps=document.getElementById('steps').checked;var res=0;var info="";if(isNaN(w)||isNaN(bw)){alert('Please enter valid numeric values');return;}if(type==='1rm'){if(isNaN(r)){alert('Please enter reps for 1RM calculation');return;}res=w*(1+(r/30));document.getElementById('resultLabel').innerHTML='Estimated One-Rep Max';document.getElementById('resultValue').innerHTML=res.toFixed(1)+' units';if(showSteps){info="95%: "+(res*0.95).toFixed(1)+"
90%: "+(res*0.90).toFixed(1)+"
85%: "+(res*0.85).toFixed(1)+"
80%: "+(res*0.80).toFixed(1);}}else if(type==='ratio'){res=w/bw;document.getElementById('resultLabel').innerHTML='Strength-to-Weight Ratio';document.getElementById('resultValue').innerHTML=res.toFixed(2)+'x';info="You are lifting "+(res*100).toFixed(0)+"% of your body weight.";}else if(type==='wilks'){var coeff;if(gen==='male'){var a=-216.0475144,b=16.2300691,c=-0.16885157,d=0.00114425,e=-0.0000032391,f=0.00000001291;coeff=500/(a+(b*bw)+(c*Math.pow(bw,2))+(d*Math.pow(bw,3))+(e*Math.pow(bw,4))+(f*Math.pow(bw,5)));}else{var a=594.3174777,b=-27.2384253,c=0.82112226,d=-0.009307339,e=0.0000473158,f=-0.00000009054;coeff=500/(a+(b*bw)+(c*Math.pow(bw,2))+(d*Math.pow(bw,3))+(e*Math.pow(bw,4))+(f*Math.pow(bw,5)));}res=w*coeff;document.getElementById('resultLabel').innerHTML='Wilks Score';document.getElementById('resultValue').innerHTML=res.toFixed(2);info="The Wilks Score compares strength across different body weights.";}document.getElementById('extraInfo').innerHTML=info;}function resetForm(){document.getElementById('extraInfo').innerHTML=";document.getElementById('resultValue').innerHTML='0.00′;updateFields();}

How to Use the Strength Calculator

The strength calculator is a versatile tool designed for powerlifters, bodybuilders, and fitness enthusiasts to quantify their physical capabilities. Whether you are trying to find your theoretical one-rep maximum (1RM), calculate how strong you are relative to your size, or determine your competitive standing using the Wilks Score, this tool provides accurate estimates based on proven sports science formulas.

To use this calculator effectively, select your desired calculation type from the dropdown menu and enter your lift data. For the most accurate 1RM results, use a weight that you can lift for 2 to 10 repetitions with perfect form.

Weight Lifted
The amount of weight used for a specific set (e.g., bench press, squat, or deadlift).
Reps Performed
The number of continuous, successful repetitions completed until technical failure.
Body Weight
Your current weight, which is essential for calculating relative strength and competition scores.

How the Calculations Work

Our strength calculator employs several different mathematical models depending on your selection:

1. One-Rep Max (Epley Formula)

The Epley formula is the industry standard for estimating how much you could lift for a single rep based on a higher-rep set. It is widely regarded as one of the most accurate models for strength athletes.

1RM = w * (1 + r / 30)

  • w: Weight lifted in the set
  • r: Number of repetitions completed

2. Strength-to-Weight Ratio

This metric is crucial for athletes in weight-classed sports. It simply divides the weight lifted by your total body weight. A common goal for the bench press is a 1.0x ratio (lifting your body weight), while elite deadlifters often aim for 2.5x to 3.0x.

3. The Wilks Score

The Wilks Coefficient is a complex polynomial equation used in powerlifting competitions to compare the strength of lifters across different weight classes. It levels the playing field, allowing a 150lb lifter to compete fairly against a 300lb lifter by calculating who is stronger relative to their physiological potential.

Calculation Example

Scenario: A male lifter weighing 180 lbs performs a set of Back Squats with 275 lbs for 5 repetitions. He wants to know his estimated 1RM and his strength-to-weight ratio.

Step-by-Step Solution:

  1. Identify Variables: Weight (w) = 275, Reps (r) = 5, Body Weight (bw) = 180.
  2. Calculate 1RM: 275 * (1 + 5 / 30) = 275 * (1.1667) = 320.8 lbs.
  3. Calculate Ratio: 275 / 180 = 1.52x body weight.
  4. Interpret Results: The lifter has an estimated max of roughly 321 lbs and is currently squatting over 1.5 times his body weight.

Common Questions

Are 1RM calculators accurate?

Calculators are highly accurate (within 3-5%) when using rep ranges between 2 and 8. As repetitions increase (e.g., a 20-rep set), the formula becomes less reliable because muscular endurance starts to play a larger role than pure neurological strength.

Why calculate 1RM instead of just testing it?

Testing a true 1RM is extremely taxing on the Central Nervous System (CNS) and carries a higher risk of injury. Using a strength calculator allows you to program your training percentages (e.g., "do 3 sets at 80% of 1RM") without needing to max out every week.

What is a good strength-to-weight ratio?

Standards vary by lift. For the Bench Press, 1.0x (body weight) is considered "Intermediate." For the Squat, 1.5x is a common benchmark for intermediate lifters, while 2.0x is considered advanced. For the Deadlift, 2.0x is intermediate and 2.5x+ is advanced.

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