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Hair Growth Calculator

Table of contents

Hair growth cycleWhat factors influence hair growth?How fast does hair grow? The formula behind hair growth calculatorHow to use the hair growth calculatorMore than the hair length calculator: see also...FAQs

Welcome to the hair growth calculator, here to help you answer the question "How much longer will my hair be in 2, 10, or 20 months from now?" or maybe "How fast does hair grow?" Even better, you'll learn about the stages of the hair growth cycle and exactly what factors influence hair growth.

Hair growth cycle

The concept of hair seems simple: it grows, it sheds (yes, your dog isn't the only one in the house who gets hair everywhere). Actually, hair growth is way more complicated than that. Hair does not grow continuously but rather in cycles. At any given time, a random number of hairs can be in any one of the three stages of the hair growth cycle, unlike our other mammalian friends whose cycles are seasonal or cyclical. These stages are known as anagen, catagen, and telogen.

  • Anagen is the active phase of hair growth where the cells in the root of the hair are dividing quickly. When a new hair forms, it pushes the other hair, called club hair, up and out of the hair follicle.

    Club hair is hair that has stopped growing or is no longer in the anagen phase. The hair on your scalp stays in the anagen phase for about 2 to 6 years! On the other hand, hair on your arms, legs, eyebrows, and eyelashes has a very short active phase of about 30 to 45 days, which explains why we would never be able to make a ponytail out of these hairs.

  • Catagen is a transitional phase that lasts about 2 weeks. Growth stops, and a club hair forms.

  • Telogen is a resting phase that lasts for about 100 days for scalp hair and longer for hairs on the rest of the body. During this phase, the hair follicle is entirely at rest, and the club hair is fully formed. About 25 to 100 of these hairs shed each day.

What factors influence hair growth?

Now that you know all about the hair growth cycle, it's time to find out exactly what factors influence hair growth:

  • Genetics: a person's genes determine how fast their hair will grow;

  • Sex: male hair grows faster than female hair;

  • Age: hair has the greatest potential to grow quickly between the ages of 15 and 30;

  • Nutrition: good nutrition is essential for healthy hair; and

  • Stress: this can cause hair to prematurely enter into the wrong stages of the hair growth cycle (i.e., going into catagen or telogen too early).

How fast does hair grow? The formula behind hair growth calculator

The average hair growth rate is 0.5 inches per month, so growth in inches per month can be calculated according to the following equation: L = 0.5 × t, where L represents the length in inches, and t represents the amount of time in months. For the average hair growth rate in centimeters or millimeters per month, 0.5 can be converted and substituted into the equation.

If you need to, you may refer to the length converter to convert between length units of your choice.

How to use the hair growth calculator

To use the hair growth calculator:

  • Enter the number of months in the first field to see how long your hair will grow during that period. For example, if you want to determine 1-year hair growth, you can enter 1 with the "year" unit into the first field, and it will calculate how many inches your hair will grow in 1 year. Perhaps you just dyed your hair, and you're curious about what your roots might look like in 6 months without a touch-up. For 6-month hair growth, enter 6 with the unit "months" into the first field to calculate how many inches your hair will grow in 6 months.

  • You can also enter a length first into the second field to determine how many months it will take for your hair to grow that length. You can freely switch between units of length without worrying about doing the conversions yourself - this is already programmed into the calculator!

  • Maybe you want to know the final length of your hair in 20 days, given the current length of your hair right now? Good news: you can also use this tool as a hair length calculator. Enter the amount of time in the first field. Then, enter the current length of your hair. That's it! The final length of your hair over the specified amount of time will be calculated for you!

More than the hair length calculator: see also...

Apart from the hair growth calculator, we have a bunch of tools (not only for a bad hair day):

  • Want to have more fun with hair? Check out our hair diffraction calculator.

  • Speaking of hair, most of us use plastic bottles of shampoo or conditioner to wash it, and those are probably not the only plastic items you find yourself using often. If you want to know your yearly or lifetime plastic footprint, you can find out with this neat plastic footprint calculator.

  • Wondering how long your new tube of mascara or eyeliner will last? Head on over to our beauty products calculator.


What is the difference between curly hair and straight hair?

There are two main differences between curly hair and straight hair: the hair shafts and the texture. The follicle of straight hair has a circular shape, while curly hair grows out of a more oval-shaped follicle. The texture of hair depends on the cuticle, which is the hard covering of the hair. In straight hair, the scales that make up the cuticle lie flat, making the surface more smooth and shiny. These scales do not lie as flat in curly hair making curly hair look and feel a bit rougher but also giving it more volume.

How much hair are we born with?

People are born with around 5 million hair follicles. About 100,000 of these hair follicles are on the scalp.

Why do we get gray hair?

Your hair follicles have cells (called pigment cells) that make melanin, a chemical that gives your hair (and eyes and skin) color. As you get older, these pigment cells die. Fewer pigment cells result in lighter hair growing in various shades of gray, silver, and eventually white.

Why do we have hair in the first place?

Hair has several purposes depending on the location. The hair on our scalp protects us from the sun, while our eyelash, eyebrow, and nose hairs protect us from bugs, dust, and other irritants. Hair is also an excellent insulator, and it can extend our sense of touch so that we can "feel" something even before it directly touches our skin. Scientists also believe it serves a social communication purpose.

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