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Three Methods:Calculate Growth RateCalculate Doubling TimeCalculate population doubling level (PDL) period

Doubling time refers to the time it takes for the growth of specific things to double, such as populations or even living cells. This knowledge can come in handy for estimating geographic areas where resources may run out because of extreme population increases at a fast rate, or estimating the growth of cancer or other detrimental cells to decide on a course of treatment. Growth rates and doubling time can also be affected by environmental resources or, in the case of medicine, antibiotics or chemotherapy. If you have the tools necessary, such as the Internet or other resources, for finding the figures for population growth rate, you can use a standard and very simple equation to estimate doubling time if you have a good calculator. Finding the growth rate of populations can be as easy as looking them up on the Internet through the census information or contacting the city, county or state government offices who can point you in the right direction. If you need to calculate growth rate, the calculation can be simple if you have some initial population counts, whether it be human population or living cells.


Method 1 of 3: Calculate Growth Rate

  1. 1
    Count or get a count of the total number today of the item to be measured for doubling time (local population, cells).
  2. 2
    Get a count of the total number of the item from a year ago (or some other point in time that can be measured).
  3. 3
    Compute the growth rate using this formula: (Present Value – Past Value) / Past Value. Multiply by 100.

Method 2 of 3: Calculate Doubling Time

  1. 1
    Divide the percentage growth rate by 100 to get a decimal numeral if not already in that format.
  2. 2
    Let "70" be the constant in the doubling equation.
  3. 3
    Let "t" represent the doubling time.
  4. 4
    Let "k" represent the growth rate.
  5. 5
    Use the equation t = 70/k.
  6. 6
    Solve for "t" by dividing 70 by "k" (the growth rate); the answer is your doubling time.

Method 3 of 3: Calculate population doubling level (PDL) period

  1. 1
    Calculate the PDL of the current passage using the following equation:
    • PDL = X + 3.322 (log Y – log I)
    • Where:
    • X = initial PDL
    • I = cell inoculum (number of cells plated in the flask)
    • Y = final cell yield (number of cells at the end of the growth period).

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  • If counting populations of such minute things as living cells, it is helpful to have a counting tool such as a grid to estimate the number of cells within a specific area; otherwise, counting can become cumbersome and time consuming. With cells, growth rate is fast because they multiply so quickly. Make sure that you use the same counting tool when measuring ending growth to get the growth rate.

Things You'll Need

  • Paper
  • Pencil
  • Internet access or other resources
  • Calculator that has logarithmic functions (logarithmic functions are necessary only if calculating initial exponential growth)
  • Counting device, such as a grid, if using small items such as cells
  • Microscope or some other magnifying unit if measuring minute items

Article Info

Categories: Mathematics

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