There are two items that need to be centered:

1. Your handlebars must be centered in the stem. And,
2. Your stem must be centered on the steer tube.

Do those two things in that order.

Centering your handlebars on the stem is the easy part. Eyeballing is usually enough. However, if you desire absolute perfection, simply find a point on the handlebars that is easily distinguishable on both sides and measure to the center of the stem (or a stem bolt if they are centered). You want an even measurement on both sides. The point that you choose on the handlebars can be anything so long as it is easily recognizable on both sides.

I'm guessing that what you're really concerned with is getting the stem aligned on the steer tube.

Once you've got the handlebars centered within the stem, center the stem on the steer tube. Again, eyeballing this is usually relatively easy. I usually do it by looking at the bike from the front, holding the front wheel between my knees, lining up the rear wheel perpendicular to my body, and aligning the handlebars perpendicular to the frame.

I have also heard people on this site talk about kicking the frame off to the side and aligning the bars perpendicular to the front wheel. The idea is that what you really want is the handlebars aligned with the front wheel and the frame is a distraction. I have tried this and it didn't work for me. I'm not saying it's a bad approach, I just think it's not the method for me.

If you absolutely need a mathematical method, the isosceles triangle measurements described in Hildred's answer should work magnificently.

You also mention measuring relative to a screw on the hoods. The hoods should be (more or less) the last thing that you align on your cockpit. Go ahead and put the on at the beginning - they'll help you to get an overview - but make centering the handlebars in the stem and the stem on the steer tube your priorities. Once you've got those in place, then it's time to fine tune your hoods. After all, your hoods should be mounted tightly enough to accommodate every day riding but loosely enough that they rotate rather than break if you fall. A pleasant side effect of this is that with a little oomph you can move them into position sans tools of they're close but not quite right.

It's also worth noting that your body is not perfectly symmetrical. No one's is. If you get everything measured out and positioned within a nanometer and it doesn't feel right, readjust it to feel right. A comfortable, easily handled steed is far more important than getting it perfect within a nano meter..

There are two items that need to be centered:

1. Your handlebars must be centered in the stem. And,
2. Your stem must be centered on the steer tube.

Do those two things in that order.

Centering your handlebars on the stem is the easy part. Eyeballing is usually enough. However, if you desire absolute perfection, simply find a point on the handlebars that is easily distinguishable on both sides and measure to the center of the stem (or a stem bolt if they are centered). You want an even measurement on both sides. The point that you choose on the handlebars can be anything so long as it is easily recognizable on both sides.

I'm guessing that what you're really concerned with is getting the stem aligned on the steer tube.

Once you've got the handlebars centered within the stem, center the stem on the steer tube. Again, eyeballing this is usually relatively easy. I usually do it by looking at the bike from the front, holding the front wheel between my knees, lining up the rear wheel perpendicular to my body, and aligning the handlebars perpendicular to the frame.

I have also heard people on this site talk about kicking the frame off to the side and aligning the bars perpendicular to the front wheel. The idea is that what you really want is the handlebars aligned with the front wheel and the frame is a distraction. I have tried this and it didn't work for me. I'm not saying it's a bad approach, I just think it's not the method for me.

If you absolutely need a mathematical method, the isosceles triangle measurements described in Hildred's answer should work magnificently.

You also mention measuring relative to a screw on the hoods. The hoods should be (more or less) the last thing that you align on your cockpit. Go ahead and put the on at the beginning - they'll help you to get an overview - but make centering the handlebars in the stem and the stem on the steer tube your priorities. Once you've got those in place, then it's time to fine tune your hoods. After all, your hoods should be mounted tightly enough to accommodate every day riding but loosely enough that they rotate rather than break if you fall. A pleasant side effect of this is that with a little oomph you can move them into position sans tools of they're close but not quite right.

It's also worth noting that your body is not perfectly symmetrical. No one's is. If you get everything measured out and positioned within a nanometer and it doesn't feel right, readjust it to feel right. A comfortable, easily handled steed is far more important than getting it perfect within a nano meter..

There are two items that need to be centered:

1. Your handlebars must be centered in the stem. And,
2. Your stem must be centered on the steer tube.

Do those two things in that order.

Centering your handlebars on the stem is the easy part. Eyeballing is usually enough. However, if you desire absolute perfection, simply find a point on the handlebars that is easily distinguishable on both sides and measure to the center of the stem (or a stem bolt if they are centered). The point that you choose on the handlebars can be anything so long as it is easily recognizable on both sides.

I'm guessing that what you're really concerned with is getting the stem aligned on the steer tube.

Once you've got the handlebars centered within the stem, center the stem on the steer tube. Again, eyeballing this is usually relatively easy. I usually do it by holding the front wheel between my knees, lining up the rear wheel perpendicular to my body, and aligning the handlebars perpendicular to the frame.

I have also heard people on this site talk about kicking the frame off to the side and aligning the bars perpendicular to the front wheel. The idea is that what you really want is the handlebars aligned with the front wheel and the frame is a distraction. I have tried this and it didn't work for me. I'm not saying it's a bad approach, I just think it's not the method for me.

If you absolutely need a mathematical method, the isosceles triangle measurements described in Hildred's answer should work magnificently.

You also mention measuring relative to a screw on the hoods. The hoods should be (more or less) the last thing that you align on your cockpit. Go ahead and put the on at the beginning - they'll help you to get an overview - but make centering the handlebars in the stem and the stem on the steer tube your priorities. Once you've got those in place, then it's time to fine tune your hoods. After all, your hoods should mounted tightly enough to accommodate every day riding but loosely enough that they rotate rather than break if you fall. A pleasant side effect of this is that with a little oomph you can move them into position of they're close but not quite right.

It's also worth noting that your body is not perfectly symmetrical. No one's is. If you get everything measured out and positioned with a micrometer and it doesn't feel right, readjust it to feel right. A comfortable, easily handled steed is far more important than getting it perfect within a nano meter.

There are two items that need to be centered:

1. Your handlebars must be centered in the stem. And,
2. Your stem must be centered on the steer tube.

Do those two things in that order.

Centering your handlebars on the stem is the easy part. Eyeballing is usually enough. However, if you desire absolute perfection, simply find a point on the handlebars that is easily distinguishable on both sides and measure to the center of the stem (or a stem bolt if they are centered). You want an even measurement on both sides. The point that you choose on the handlebars can be anything so long as it is easily recognizable on both sides.

I'm guessing that what you're really concerned with is getting the stem aligned on the steer tube.

Once you've got the handlebars centered within the stem, center the stem on the steer tube. Again, eyeballing this is usually relatively easy. I usually do it by looking at the bike from the front, holding the front wheel between my knees, lining up the rear wheel perpendicular to my body, and aligning the handlebars perpendicular to the frame.

I have also heard people on this site talk about kicking the frame off to the side and aligning the bars perpendicular to the front wheel. The idea is that what you really want is the handlebars aligned with the front wheel and the frame is a distraction. I have tried this and it didn't work for me. I'm not saying it's a bad approach, I just think it's not the method for me.

If you absolutely need a mathematical method, the isosceles triangle measurements described in Hildred's answer should work magnificently.

You also mention measuring relative to a screw on the hoods. The hoods should be (more or less) the last thing that you align on your cockpit. Go ahead and put the on at the beginning - they'll help you to get an overview - but make centering the handlebars in the stem and the stem on the steer tube your priorities. Once you've got those in place, then it's time to fine tune your hoods. After all, your hoods should be mounted tightly enough to accommodate every day riding but loosely enough that they rotate rather than break if you fall. A pleasant side effect of this is that with a little oomph you can move them into position sans tools of they're close but not quite right.

It's also worth noting that your body is not perfectly symmetrical. No one's is. If you get everything measured out and positioned within a nanometer and it doesn't feel right, readjust it to feel right. A comfortable, easily handled steed is far more important than getting it perfect within a nano meter..