How To Measure Biceps (Flexed Or Relaxed) At Home

So you want to know how big your arms actually are.

Maybe you're tracking your gym progress. Maybe you're buying a fitted shirt and tired of guessing. Or maybe someone at the gym mentioned their "17-inch arms" and you went home wondering where yours stand.

Whatever the reason, you're in the right place.

Measuring biceps (aka guns) sounds simple, wrap a tape around your arm, done. But there's more to it than that.

Most people do it wrong and end up with numbers that are either inflated or inconsistent. 

This guide will fix that.

What You Need Before You Measure Your Biceps

You don't need anything fancy. Just one tool:

A flexible measuring tape. The kind tailors use. Soft, bendy, and long enough to wrap around your arm without pulling.

That's it.

If you don't have one, grab a piece of string, wrap it around your arm, mark where it meets, and measure that length against a ruler. Not perfect, but it works.

One more thing, measure on bare skin. Measuring over a sleeve adds extra thickness and throws off your numbers.

How to Measure Biceps the Right Way (Relaxed Method)

This is the standard method. The one used in fitness studies, CDC data, and most size comparisons you'll find online.

Here's how to do it:

Step 1: Stand straight. Let your arm hang naturally at your side. Palm facing forward.

Step 2: Find the midpoint between your shoulder tip and your elbow. This is roughly where your bicep is fullest.

Step 3: Wrap the tape measure around that point. Keep it level — parallel to the floor.

Step 4: Make sure it's snug, not tight. You shouldn't be squeezing the muscle.

Step 5: Read the number. Write it down.

Step 6: Do the same for the other arm.

Yes, both arms. Most people have a slight size difference between their dominant and non-dominant arm, and that's completely normal.

How to Measure Flexed Biceps

This is the fun one. The ego measurement. The one bodybuilders use on stage.

Step 1: Sit at a table and rest your elbow on it.

Step 2: Make a fist and curl your forearm up toward your shoulder like you're doing a bicep curl.

Step 3: Flex as hard as you can.

Step 4: Wrap the tape over the highest peak of your bicep — the very top of the muscle.

Step 5: Read and record.

Your flexed number will always be larger than your relaxed number. That's expected. Just be consistent, always compare flexed to flexed and relaxed to relaxed when tracking progress.

Flexed vs Relaxed: Which Bicep Measurement Actually Matters?

Both, depending on what you're measuring for.

Use relaxed measurements when comparing your arms to average size charts or CDC data. All population-based averages use relaxed measurements, so if you compare your flexed number to an average relaxed number, you're going to get a skewed result.

Use flexed measurements when tracking personal muscle growth over time. Flexed numbers respond more visibly to training progress, which makes them motivating.

Pick one method, stick with it every time, and you'll have data you can actually trust.

Where Exactly on the Arm Should You Measure?

This trips a lot of people up.

You measure at the thickest point of your upper arm. For most people, this is roughly halfway between the shoulder and the elbow, maybe slightly closer to the shoulder.

A quick trick: gently squeeze along your upper arm while it's relaxed. You'll feel where the muscle is fullest. That's your spot.

Don't measure too close to the armpit. Don't measure near the elbow. The thickest point only.

Common Bicep Measurement Mistakes to Avoid

You'd be surprised how many people mess this up.

Measuring right after a workout

Your muscles are pumped with blood after training, which temporarily inflates the size. Wait a few hours, or measure in the morning before hitting the gym.

Flexing when you should be relaxed

If you're comparing to average size charts, your measurement needs to be relaxed. Even a slight tension changes the number.

Pulling the tape too tight

It compresses the muscle and gives you a smaller reading. Snug but comfortable is the rule.

Measuring in different spots each time

If you measure two inches higher this week than last week, your progress data means nothing. Be consistent with the location.

Only measuring one arm

Always measure both. If there's a big difference, that's worth knowing, it could point to a muscle imbalance you should address in your training.

Average Bicep Size by Age: How Do You Compare?

Now, the part everyone actually wants to know (average bicep size).

These numbers come from CDC data and represent relaxed arm circumference, which includes both muscle and fat tissue, not just the bicep muscle alone.

Average bicep size for men:

Average bicep size for women:

Arms tend to peak in your mid-30s and gradually decrease after that, unless you're actively training and eating enough protein to maintain muscle.

What Is Considered a Good Bicep Size?

Here's a rough guide for men (flexed):

• 11 to 12 inches — Beginner range. Room to grow.
• 13 to 14 inches — Average gym-goer.
• 15 to 16 inches — Noticeably muscular. You've put in real work.
• 17 to 18 inches — Impressive. Turns heads at the gym.
• 18 to 20 inches — Elite level. Serious training and genetics.

For women (flexed):

• 11 to 12 inches — Lean and toned.
• 13 to 14 inches — Visibly strong and athletic.
• 15 to 16 inches — Bodybuilding territory.

Eager to grow your biceps? 

How Often Should You Measure Your Biceps?

Once every four weeks is the sweet spot.

Any more frequent than that and you won't see meaningful change, muscle growth is slow. Any less and you might miss what's working (or not working) in your training.

Pick the same day, same time of day, same arm position, every single time. First thing in the morning before eating or working out is ideal. Your muscles are consistent at that point, not pumped, not depleted.

Write the numbers down. Use a notes app, a spreadsheet, whatever works for you. The data is useless if you can't look back at it.

How to Measure Biceps for Shirt Sizing

This is slightly different from fitness measurements, and it's worth knowing the difference.

When measuring for clothing, you want your arm relaxed and hanging at your side. Wrap the tape around the fullest part of your upper arm, usually about two to three inches below the armpit.

Don't flex. Clothes are worn on relaxed arms.

Add about a quarter inch to the measurement for comfort and ease of movement. If you're between two sizes, always go with the larger one.

There's nothing worse than a shirt sleeve that cuts into your arm when you reach for something.

Tips to Get the Most Accurate Bicep Measurement

A few final things that make a real difference:

Get someone else to measure you

It's genuinely difficult to hold the tape perfectly level on your own arm. A second pair of hands gets you a more accurate number.

Measure at the same time each day

Your body changes throughout the day. Morning measurements before food and training are the most consistent.

Use the same tape measure every time

Different tapes can have minor variations. Stick to one.

Don't round down

If it lands between 14 and 14.5 inches, record 14.5. Rounding down feels modest but gives you bad data.

Final Thoughts

Measuring your biceps isn't complicated, but doing it right makes a big difference, whether you're tracking gym progress or buying clothes that actually fit.

The rules are simple: use a flexible tape, find the thickest point of your upper arm, stay consistent with your method, and measure regularly.

By the way, do you know why your biceps are not growing?