A single human arm, shoulder to fingertips, weighs about 5% of your body weight. For most adults that works out to roughly 8 to 10 pounds (3.5 to 4.5 kg) on each side, a bit more in men and in muscular people. You rarely notice it, because your muscles hold it up for you almost all day. Arm weight shows up mostly when something changes: reaching overhead for a long time, swelling, or wearing an artificial arm.
How to Work Out Your Own Arm’s Weight
Each part of the arm is a fairly fixed share of body weight on average:
- Upper arm (shoulder to elbow): about 2.9% of body weight.1Aerospace Medical Research Laboratory. Weight, Volume, and Center of Mass of Segments of the Human Body
- Forearm (elbow to wrist): about 1.8%.2Aerospace Medical Research Laboratory. Weight, Volume, and Center of Mass of Segments of the Human Body
- Hand: about 0.7%.3Aerospace Medical Research Laboratory. Weight, Volume, and Center of Mass of Segments of the Human Body
- Whole arm: all three added together come to about 5.4%.
To do the calculation, take your body weight and multiply it by 0.054. That gives the weight of one arm. If your scale reads in pounds, the answer comes out in pounds; if it reads in kilograms, you get kilograms, so there’s no need to convert first. To switch units afterward, divide pounds by 2.2 to get kilograms, or multiply kilograms by 2.2 to get pounds. A quick shortcut for your phone is one-twentieth of your body weight, which lands very close to the 5.4% figure. Double the result for both arms, which is roughly a tenth of your body weight. If you only care about the hand or forearm, such as for a wrist injury, use those separate shares instead.
A few examples show how it plays out. A 150-pound person has an arm weighing about 8 pounds. At 200 pounds, one arm weighs about 10.8 pounds. For a 70 kg person, one arm is about 3.8 kg, and the hand is about half a kilo of that. The hand alone averages about 400 grams, not counting the forearm muscles that move the fingers.4IEEE International Conference on Rehabilitation Robotics. Performance Characteristics of Anthropomorphic Prosthetic Hands The upper arm holds more than half the total, so most of the weight sits near the shoulder.
Treat your result as an estimate. The percentages describe an average body, and yours may differ. No home method measures a living arm exactly, so round freely.
The shares also help with questions about a cast, sling or wrist brace. The forearm and hand together are about 2.5% of body weight, which is the weight hanging below the elbow. For a 180-pound person that’s roughly 4.5 pounds, which helps explain why a sling can feel like relief even though the arm seems light.
Why Arm Weight Varies From Person to Person
Men and women build arms from different mixes of tissue. A typical man’s forearm is about 72% muscle, 15% fat and 13% bone.5PubMed. The relative proportions of fat, muscle and bone in the normal human forearm as determined by computed tomography A typical woman’s forearm is about 59% muscle, 29% fat and 12% bone.6PubMed. The relative proportions of fat, muscle and bone in the normal human forearm as determined by computed tomography Men also carry about 33 kg of muscle on average versus 21 kg in women.7PubMed. Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr That gap is larger in the upper body, about 40%, than in the legs, about 33%.8PubMed. Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr So a man’s arms usually make up a slightly bigger share of his body weight than a woman’s.
Muscle is denser than fat, so a lean arm weighs more than a fatty arm of the same size. Two people can have arms that look identical in the mirror or measure the same with a tape, yet one weighs more because more of it is muscle. Strength training can add weight even when the arm looks only a little bigger.
When your body weight changes, your arms change with it. Gaining or losing body fat takes some of that change from the arms, and because the arm stays a fairly steady share of the body, recalculating with your new weight gives a reasonable updated figure. If you build a lot of upper-body muscle, your arms may take a slightly larger share than average, so the 5.4% figure may run a bit low for you.
Your two arms are not identical either. Arms used heavily for one-sided sport grow heavier on the playing side.9PubMed. Bone mass in prepubertal tennis players Young tennis players’ racket arms were about 7.5% heavier than their other arm, from extra muscle and denser bone.10PubMed. Bone mass in prepubertal tennis players Small differences between sides are normal. A noticeably bigger difference with no sport or job to explain it is worth mentioning to a doctor.
Why Holding Your Arm Out Feels So Heavy
Where the weight sits matters as much as how much there is. The upper arm’s balance point sits a little less than halfway from shoulder to elbow.11Aerospace Medical Research Laboratory. Weight, Volume, and Center of Mass of Segments of the Human Body The forearm’s balance point sits about 41% of the way from elbow to wrist.12Aerospace Medical Research Laboratory. Weight, Volume, and Center of Mass of Segments of the Human Body With the arm straight out, the weight of the forearm and hand therefore acts far from the shoulder. The shoulder joint feels a twisting load from the arm’s own weight, which engineers estimate from height and body weight.13PubMed Central. Evaluation of fatigue progression during overhead tasks and the effects of exoskeleton assistance
You can feel this yourself. Hold your arm straight out to the side and the shoulder will likely burn within a minute or two. Now bend the elbow and bring the hand toward your shoulder, and the same arm feels lighter. It didn’t lose weight; the same weight is acting over a shorter distance, so the shoulder has less twisting to resist. Keeping elbows tucked in is a simple way to ease the load when painting a ceiling or holding a phone overhead.
A few habits help during arm-raised tasks. When typing or holding a tablet, rest your elbows on a desk, armrest or your lap so a surface carries some of the weight. For overhead jobs, a step stool lets you work at about shoulder height instead of above it. Short breaks help too, because shoulder fatigue builds steadily, and stopping before the burn gets strong lets the muscles recover sooner.
Arm weight also helps when you move. Swinging arms act like counterweights that steady the upper body while walking and running.14Journal of Experimental Biology. Control and Function of Arm Swing in Human Walking and Running Adding weights to the arms or removing their swing changes how much the head and shoulders twist.15Journal of Experimental Biology. Control and Function of Arm Swing in Human Walking and Running
How Prosthetic Arms Compare
A well-designed powered adult prosthetic arm can weigh as little as about 1 kg, roughly a quarter of a natural arm.16bme240.eng.uci.edu. Considerations Powered arms with motors and batteries are heavier than cosmetic or cable-operated ones.17bme240.eng.uci.edu. Considerations Even so, about 79% of powered-hand users say their device is too heavy.18IEEE International Conference on Rehabilitation Robotics. Performance Characteristics of Anthropomorphic Prosthetic Hands Users rank weight near the top of what they want improved, about 70 on a 100-point importance scale.19IEEE International Conference on Rehabilitation Robotics. Performance Characteristics of Anthropomorphic Prosthetic Hands
The reason is how the weight is carried. A natural arm’s weight is borne by bone, joints and muscles attached directly to the body, which are built for that load. A prosthesis hangs from a socket and straps that grip the remaining limb, so its weight pulls on skin and soft tissue instead.20IEEE International Conference on Rehabilitation Robotics. Performance Characteristics of Anthropomorphic Prosthetic Hands Soft tissue isn’t built for a steady pull, so even a light device can cause pressure, rubbing and tiredness over a long day. Implants anchored into bone, available at some specialist centers, let the skeleton carry the load instead.
When choosing a prosthesis, ask the clinician for the device’s total weight including the battery, since the battery can be a large part of it. Try a device for a full day if possible, because discomfort and fatigue often only show up after several hours. A simpler hand that does less may be more comfortable to wear all day, so weigh extra features against extra weight, and tell the clinician which daily tasks matter most to you.
When an Arm Gets Heavier From Swelling
Lymphedema is lasting arm swelling that can follow breast cancer surgery when lymph drainage is damaged. A swollen arm can hold 73% more fat, 47% more muscle and 7% more bone than the other arm.21PubMed. Breast cancer-related chronic arm lymphedema is associated with excess adipose and muscle tissue The swollen arm therefore weighs noticeably more, and it stays heavier even when the fluid is managed. Losing body weight after treatment did not lower the chance of developing this swelling.22PubMed Central. Weight loss does not decrease risk of breast cancer-related arm lymphedema
Lymphedema often starts as a feeling that the arm is full, tight or heavy, particularly late in the day. A ring, watch or sleeve that suddenly feels tight on one side is a common early clue, even if the swelling is hard to see. Anyone who has had breast cancer treatment and notices these changes should see a doctor promptly, because treating it early generally works better. Sudden swelling with pain, warmth or redness needs same-day medical care, since it can mean an infection or a blood clot.
The usual treatments are compression garments and therapy from a specialist trained in lymphedema, which target the fluid directly. They manage the swelling but don’t remove the extra fat and muscle, which fits with the arm staying heavier.
Accounting for a Missing Arm in Body Weight
Standard weight measures assume a full body. Doctors use formulas that add back a missing limb’s share to estimate full body weight and BMI.23PubMed. Method for estimating body weight in persons with lower-limb amputation and its implication for their nutritional assessment A whole missing arm removes about 5.4% of expected body weight.
To adjust, divide your scale weight by 0.946 for a whole missing arm. For a missing hand only, divide by about 0.993, since the hand’s share is 0.7%. A person who reads 142 pounds with one arm missing has an adjusted weight of about 150 pounds. Ask your clinician which adjustment they use so your records and theirs match.
If you use a prosthesis, choose one weighing routine, either always with the device or always without it, so your numbers are comparable over time. If you step on the scale wearing it, subtract its weight first, which is one more reason to know the device’s total weight.