Ever wondered how to calculate your weight without weighing machine? It’s a common situation, whether you’re traveling, at home without a scale, or just curious. You can get a good estimate using some clever math and everyday objects.
How To Calculate Your Weight Without Weighing Machine
This method relies on physics, specifically the principle of levers. It’s simple and only requires a few things you probably already have. The basic idea is to balance yourself against a known weight.
What You’ll Need
- A long, sturdy board (like a 2×4 or a broom handle).
- A fulcrum (the pivot point). This can be a brick, a sturdy box, or a similar object.
- A known weight. A bag of flour or sugar, unopened water bottles, or dumbbells work perfectly. Make sure you know it’s exact weight.
- A measuring tape or ruler.
The Step-by-Step Balancing Method
Follow these steps carefully for the most accurate result.
- Set Up Your Seesaw: Place your fulcrum on a flat, hard surface. Balance the long board across it so it looks like a seesaw. The board should be level.
- Position the Known Weight: Place your known weight on one end of the board. For example, a 5kg bag of flour. Move it until that end of the board touches the ground and the other end is up in the air.
- Mark the Balance Point: Now, you need to find where you must sit to balance the known weight. Carefully get on the board on the opposite end. Slide yourself closer to or farther from the fulcrum until the board becomes perfectly level and balanced. Have a friend mark the spot where you are sitting.
- Measure the Distances: Get off carefully. Use your measuring tape to find two distances:
- Distance A: From the fulcrum to the center of the known weight.
- Distance B: From the fulcrum to the mark where you were sitting.
- Do the Math: Use this simple formula:
(Your Weight) = (Known Weight) x (Distance A / Distance B).
So, if your known weight is 5kg, Distance A is 30cm, and Distance B is 120cm, your weight = 5 x (30/120) = 1.25kg. That’s clearly wrong because we forgot something crucial: this gives your mass in the same unit as your known weight. Multiply that answer by the gravitational constant (9.8 m/s²) to get your weight in Newtons, but that’s not helpful. Actually, the formula works directly if you use the same units. The correct calculation is 5kg x (30/120) = 1.25kg? Wait, that can’t be right. Let’s recalculate. If you are farther from the fulcrum than the weight, you should weigh less. In our example, you are at 120cm and the weight is at 30cm. The weight is closer, so it feels heavier. So your weight = 5kg x (120/30) = 20kg. That’s still off. The correct formula is (Your Weight) x (Your Distance) = (Known Weight) x (Its Distance). So, Your Weight = (Known Weight x Known Distance) / Your Distance. So 5kg x 30cm / 120cm = 1.25kg. That’s the mass. To get an estimate in kilograms, the formula actually works if distances are measured correctly. I’ve confused the setup. Let’s clarify: When balanced, the product of weight and distance on both sides are equal.
For better clarity, here’s the infalible formula:
(Weight of Object) x (Distance from Fulcrum to Object) = (Your Weight) x (Distance from Fulcrum to You).
Therefore, Your Weight = (Weight of Object x Distance from Fulcrum to Object) / Distance from Fulcrum to You.
Using the earlier numbers: Your Weight = (5kg x 30cm) / 120cm = 150 / 120 = 1.25 kg. This is obviously incorrect for a person’s mass, indicating the known “weight” used was too light or distances were measured inaccurately. You need a heavier known object, like a person with a known weight, for this method to work well. A 20kg weight would give a more reasonable result.
Using Water Displacement
This method estimates volume, which you then convert to weight. It’s less direct but can provide a rough idea.
- Fill a bathtub to the very brim.
- Gently get into the tub, allowing the water to overflow into a collection area or just noting how much the water level drops.
- Carefully get out without causing more splashes.
- Measure the volume of water that overflowed (or refill the tub with a measured bucket to the original brim line). This volume is roughly equal to your body’s volume.
- The average density of the human body is close to that of water (985 kg/m³). So, your weight in kilograms is approximately equal to your volume in liters. If you displaced 70 liters of water, your mass is roughly 70kg. To get weight, multiply mass by gravity (9.8), but for a quick estimate in “kg” which is actually mass, the liter-to-kg approximation is handy.
Important Limitations
- This is very messy and imprecise.
- Bone density and body composition affect the result.
- It’s hard to measure the water volume accurately.
Estimation Using Body Measurements
For a rough estimate, you can use formulas based on body circumferences. These are used in some medical and fitness fields to estimate body fat and lean mass.
You will need a flexible measuring tape.
- Measure your waist at the narrowest point.
- Measure your hips at the widest point.
- Measure your neck at the narrowest point.
- For women, an approximate formula is:
(163.205 x log10(waist + hip – neck)) – (97.684 x log10(height)) – 78.387. This gives lean body mass in pounds. Then you need to add estimated fat mass, which makes it complex.
Because these formulas are complex and gender-specific, it’s easier to use an online U.S. Navy body fat calculator. You input your height, neck, waist, and hip measurements, and it gives an estimated body fat percentage and weight range. It’s not perfect, but it’s a decent ballpark figure if you have no other options.
The Clothing Comparison Method
This is a very subjective but common way to gauge changes. It’s not a calculation, but a tracking tool.
- Choose a “benchmark” outfit—a pair of jeans, a belt, or a fitted shirt.
- Note how it fits you regularly.
- Periodically try it on. Changes in fit (looser or tighter) can indicate weight loss or gain, even if you don’t know the exact number.
- This method tells you about change, not your starting point, unless the cloths had a known size and weight correlation from when you bought them.
Smartphone Apps and Sensors
Some newer smartphone features claim to estimate weight. They might use the phone’s accelerometer or barometer when you jump or perform a movement. These are highly experimental and not reliable. Do not depend on them for any medical or fitness purposes. Their accuracy is often very poor and they are more of a novelty.
Frequently Asked Questions (FAQ)
Can I use a ruler instead of a measuring tape for the balance method?
Yes, absolutely. Any tool that can measure distance consistently will work. A 12-inch ruler is fine, you might just have to measure in segments.
How can I find out my weight without a scale at all?
The most accessible way is the balancing method with a heavy known weight. Alternatively, you can visit a public place that has a scale, like a gym, pharmacy, or some train stations.
Is there a way to calculate my weight using my height?
Height alone cannot determine weight. However, Body Mass Index (BMI) charts show weight ranges for given heights that are considered healthy. This gives you a target range, not your current weight. For example, a 5’9″ adult has a healthy weight range of about 128 to 162 pounds.
What household items can I use as a known weight?
Look for items with their mass printed on them: unopened bags of pet food (10kg, 20kg), large water jugs (the 5-gallon ones weigh about 18kg when full), or multiple packs of bottled water taped together. A dumbbell with the weight marked is ideal.
Why did my balancing method result give a number that was way to low?
This is a common error. It usually means your known weight was too light relative to you, making the distances very extreme and hard to measure precisely. Or, you might have swapped the distances in the formula. Always double-check your measurements and use the heaviest known object you can safely manage.
Can my bathroom scale be used to calibrate a homemade method?
If you have access to a bathroom scale, even briefly, you can simply weigh yourself on it. The point of these methods is for when a scale is truly not available. But yes, you could use it to weigh an object to then use as your “known weight” for later.
Remember, all these methods for how to calculate your weight without weighing machine are estimates. They are great for satisfying curiosity or tracking relative change when a proper scale isn’t around. For medical or precise fitness tracking, investing in a good quality scale is always the best course of action. The balancing method, done carefully with a sufficiently heavy object, is likely the most accurate DIY approach you can try at home. Just take your time with the measurements and the math to avoid simple slips.