Select the race distance to project total time savings.
Estimated Ideal Racing Weight
155 lbs
Based on modified Stillman Formula
-20 lbsWeight to Lose
40 sec/milePotential Pace Gain
08:44Total Race Time Saved
44:02Projected Finish Time
Formula Used: The calculation uses the Stillman height/weight ratio for runners.
Estimate: ~2 seconds per mile faster for every pound lost (above ideal weight).
Weight Loss
New Weight
Pace (min/mile)
Projected Finish Time
Understanding the Livestrong Ideal Running Weight Calculator
Achieving peak performance in running often involves finding the optimal balance between power and weight. The livestrong ideal running weight calculator is a specialized tool designed to help runners estimate their most efficient racing weight based on established physiological formulas. Whether you are training for a 5K or a marathon, understanding how body mass influences running economy is a critical component of strategic training.
What is the Livestrong Ideal Running Weight Calculator?
The livestrong ideal running weight calculator is a digital estimation tool that uses biometric data—specifically height and gender—to determine a theoretical "ideal" weight for competitive distance running. Unlike standard BMI calculators which focus on general health, this calculator focuses on performance optimization.
It is primarily intended for:
Competitive Runners: Athletes looking to shave seconds or minutes off their personal bests.
Endurance Athletes: Individuals training for marathons or triathlons where efficiency is paramount.
Coaches: Trainers helping athletes set realistic body composition goals.
Note: A common misconception is that "lighter is always faster." While reducing excess body fat can improve speed, dropping below a healthy weight can lead to injury, loss of muscle mass, and decreased performance. This calculator provides a target based on statistical averages for elite runners, not a medical prescription.
Formula and Mathematical Explanation
This calculator utilizes the Stillman Height/Weight Ratio, a formula frequently cited in running literature (including Livestrong and Runner's World) to estimate the weight of competitive distance runners. It also applies the widely accepted "2 seconds per mile per pound" rule to estimate time savings.
The Stillman Formula
The Stillman formula calculates a baseline weight for a person of a specific height, assuming a lean, runner-like build.
Gender
Base Weight (for 5 ft)
Additional Weight
Male
110 lbs
5.5 lbs per inch over 5 ft
Female
100 lbs
5.0 lbs per inch over 5 ft
The Pace Improvement Formula
Once the ideal weight is determined, the calculator estimates potential speed gains using the following logic:
Variable: Weight Loss (lbs) = Current Weight – Ideal Weight
Rule of Thumb: For every 1 lb lost, a runner gains approximately 2 seconds per mile in speed.
Total Time Saved: (Weight Loss × 2 seconds) × Race Distance (miles).
Practical Examples
Example 1: The Marathon Runner
Scenario: John is a male runner, 5'10" (70 inches), currently weighing 175 lbs. He runs a marathon in 4 hours (9:09/mile pace).
Pace Improvement: 15 lbs × 2 sec/lb = 30 seconds per mile faster.
New Pace: 7:33/mile.
5K Time Savings: 30 sec × 3.1 miles = ~1 minute 33 seconds.
Projected Time: ~23 minutes 27 seconds.
How to Use This Livestrong Ideal Running Weight Calculator
Enter Your Gender: Select Male or Female to adjust the Stillman formula baseline.
Input Height: Enter your height in feet and inches accurately.
Input Current Weight: Enter your weight in pounds. Be honest for accurate results!
Set Current Pace: Input your current average race pace (minutes and seconds per mile).
Select Race Distance: Choose your target event (5K, 10K, Half, or Full Marathon).
Analyze Results: Review your estimated ideal weight, potential time savings, and the dynamic chart showing your performance curve.
Key Factors That Affect Running Weight Results
While the livestrong ideal running weight calculator provides a mathematical target, several real-world factors influence your actual ideal racing weight:
1. Body Composition
Two runners can weigh the same but have vastly different body fat percentages. Muscle is denser than fat. A runner with higher muscle mass may weigh more than the Stillman formula suggests but still be incredibly fast and efficient.
2. Age and Metabolism
As runners age, maintaining the extremely lean weight suggested by the Stillman formula becomes more difficult and potentially less healthy. Older runners often perform better at a slightly higher weight that supports recovery and immune function.
3. Frame Size
The formula assumes a "medium" frame. Runners with broader shoulders or denser bone structures may find the calculated weight unrealistic. It is often wise to treat the result as a range (+/- 5-10%).
4. Hydration and Glycogen
Weight fluctuates daily due to water retention and glycogen stores. A "race weight" achieved through dehydration is detrimental to performance. True racing weight is a well-hydrated, fueled state.
5. Injury Risk
Running too light increases the risk of stress fractures and hormonal imbalances (such as RED-S). The financial cost of injury—physical therapy, time off work, medical bills—far outweighs the benefit of shaving a few seconds off a race time.
6. Nutritional Needs
To train hard, you must eat enough. Caloric deficits required to reach a theoretical "ideal" weight can compromise training energy. The best weight is the one at which you can train consistently without illness or injury.
Frequently Asked Questions (FAQ)
1. Is the Livestrong ideal running weight calculator accurate for everyone?
No. It is a statistical estimation based on elite runner averages. It does not account for individual muscle mass, bone density, or health history. Use it as a guideline, not a rule.
2. Will losing weight always make me faster?
Not necessarily. If weight loss comes from muscle tissue or results in fatigue, you will likely get slower. Power-to-weight ratio is key; you want to lose non-functional mass (excess fat) while maintaining power (muscle).
3. How much weight should I lose per week?
Most sports nutritionists recommend losing no more than 0.5 to 1 pound per week to ensure the weight lost is fat, not muscle, and to maintain training energy levels.
4. What if my calculated ideal weight seems too low?
Trust your body. The Stillman formula is known for producing very lean targets. If you feel weak or constantly hungry at that weight, your personal ideal running weight is likely higher.
5. Does this calculator apply to sprinters?
No. Sprinters require significantly more muscle mass for explosive power. This calculator is specifically designed for distance runners (5K to Marathon).
6. Can I use this for trail running?
Trail running often requires more strength and durability than road running. Trail runners might benefit from being slightly heavier than the calculator suggests to handle rugged terrain and elevation changes.
7. How does weight affect VO2 Max?
VO2 Max is measured in milliliters of oxygen per kilogram of body weight per minute. Therefore, reducing body weight (the denominator) while maintaining oxygen uptake (the numerator) mathematically increases your VO2 Max score.
8. Should I diet during race week to hit my weight?
Absolutely not. Race week is for fueling and tapering. Restricting calories before a race will deplete glycogen stores, leading to "hitting the wall" earlier. Focus on weight management during the base training phase.