Above is a moment of inertia swing weight calculator to be done in the comfort of your chair. Enter the information requested. For details on the data points please see below.

## Video Explanation

## Overview

Knowing the swing weight of a baseball or softball bat is vitally important when shopping, comparing and reviewing the thousands of bats available. Yet bat manufacturers do not reveal that data to the public.

With just a few metrics, however, the Moment of Inertia Swing Weight Calculator above can calculate your bat’s swing weight (MOI). You only need a **stop watch**, **measuring tape** and, if you have one, **digital (kitchen?) scale**. With your data points and thousands others like it we hope to compile a library of swing weights.

Help us improve and increase our knowledge of available bats by using the moment of inertia swing weight calculator above. Instructions are below. Or browse the other bats already submitted to the database.

**Step #1 Calculating Pendulum Period of your Bat**

This is the most difficult step.

A “period” of the pendulum is how long it takes for the bob of the pendulum to get from one extreme (1) to the other extreme (3) **AND BACK AGAIN (5)**. The picture below describes it best.

A Full Period of a Pendulum Swing is the time it takes for the ‘bob’ to get from one extreme (1), the other (3), and back again (5).

- Hold your bat in a position that lets it swing like a pendulum with the knob resting as gently as possible on top of your thumb and index finger. To stabilize, rest your pinky and ring finger on a desk or table in front of you as well as your elbow on your knee. If you are doing it correctly the bat should swing from side to side with ease.
- Push the bat to one side and let it begin to swing. Do not let the bat bounce into your palm (or anything else for that matter). Any bump or sudden movement on your part means you need to start over.
- Press start on your watch as the bat swings to one extreme (1). As the bat makes it back to the place it began (5) say “one.”
*DO NOT SAY “ONE” WHEN YOU START THE WATCH OR YOU WILL ONLY MEASURE NINE PERIODS.* - Once you’ve counted off to “ten” press stop on your watch. The closer you can start and stop your watch to the extreme (1) and (5) more consistent your number will be.
**Repeat this process at least three more times.** - Add the total times you’ve come up with and divide it by the total number of cycles you’ve measured (e.g. 5 cycles of 10 would require you divide the summed times by 50). Once divided, that result is your bat’s pendulum period. If the bat is of common size and weight your pendulum period should be somewhere between 1.2 and 1.8 (roughly).
- If you are having trouble see this example here.

**Step #2: Measure the Bat’s Balance Point**

Find the balance point of a bat by using your finger (see picture at right). Mark the spot where the bat balances and measure the distance between that mark and the end of the knob of the bat. Get as accurate a number as possible.

**Step #3: Weighing the Bat**

You should not assume that the stated weight on your bat is the actual weight of the bat. In fact,** it is uncommon the two are the same **(like I said, stated weight on a bat is pretty much useless)**. **A bat almost always weighs more than its stated weight.

If you have a kitchen scale or digital scale that measures in ounces available find a way to balance it on the scale to give you a reading.

If you do not have a scale then you can fudge the weight by adding between 1/2 and 1 1/2 ounces to the stated weight. (Kitchen scales are handy and not very expensive.) Do realize your swing weights will be off proportional to your mistake.

**Step #4: Enter Numbers In the Calculator Above**

Take the data points you have as well as the information about the bat and input it in the calculator above. It does require each field to be filled out to manufacture a result. Numbers need to be in decimals (not fractions). The database is constantly updated so any data you submit should be there within the next few days. Even if you see your bat’s data already in the sheet please submit it again so we can confirm. The more data we can gather and share the better.

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