How to give an appropriate tip in America?

Appropriate tips in America's restaurants is
10 to 20 percent of the total cost of the meal

I always tip unless the service and the food is horrible. If the food and service is horrible, I won't leave a tip.

I'll agree with that. I actually go above the 20% at the local Denny's. I almost always get outstanding service, and with my cheap breakfast, 20% really isn't much, considering that it's about the same labor as serving a T-bone.

How about taxicabs and hotels?

If I purchase something - I pay the 'purchase' price.
Never encountered 'tipping'. It is absurd.

Are you seriously saying that you have never given a tip, or encountered the phenomenon of giving a tip in a restaurant?

I have never been able to afford to eat in a restaurant - So, Yes, I am.

So you have never, ever encountered tipping?

Anywhere?

You must have heard of it though, right?

Never encountered it - And I worked in restaurants, once.
Of course I'm aware of it - US tv is available here in Wales.
Tipping is a surcharge.
If I buy something at the asking price - Why would I pay more because I'm pleased with how it was delivered?

In the US - you tip typically about 15- 20% if the service is good - closer or more to 20% if very good. If not so good closer or less than 15%. It is highly suggested that if you get poor service or have an issue to ask to speak with a manager - the manager is in a position to remedy the situation and make your dining experience better.

It serves (pun intended) no purpose to not leave a tip at all. More likely the server will think you are a cheapskate or else unfamiliar with our tipping customs and it won't help your dining experience. Telling a manager will cause the manager to help you out so you enjoy yourself and also provide the manager feedback so s/he can help the waitstaff improve on their service.

If you are asking about other countries = You could just do a google or other internet search on tip customs in XYZ country to find out what the custom is and who you should tip and how much. It does vary greatly.

When I traveled abroad when I was younger (don't have time or money for it too much now) - I used to always get a book on the area I was traveling so I would be prepared for all sorts of things - including tipping customs. Now with the internet you are just a click away from this sort of information.

When I travel abroad I try to be respectful of the country I am visiting. That means seeing what customs they have (even if it seems absurd to me) including tipping so I do not offend them.

It is just plain respect for other people and their culture.

Not tipping in the US is similar to actually causing someone to lose money. Waitstaff in most US states are paid an amount lower than the typical minimum wage with the assumption that they earn a good deal in tips. There W-2 form which is reported to IRS for filing taxes actually includes an amount for tips that is usually estimated by the manager - if you do not tip, they get charged taxes on income that they do not make and would end up costing them money.

So if you are ok morally with stiffing a person on their earnings, and causing them to pay you in a sense to work (simply because you do not agree with another culture's custom) then go you are of course free to do so. Myself, I couldn't do it.

How am I responsible for paying the wages of anyone?
If I buy a donkey for 50 quid, I expect a donkey for 50 quid.
I'm not accountable for the wages of the guy/gal who fed it, delivered it or mucked out its stable.
I bought a donkey - Not the labour aspects of its owners' employees.

In fact, after further consideration, it is you that enables the practice of employers Not paying decent wages to their employees - by doing it for them...

Thanks Linkat for bringing the topic back around to something useful.

Based on the inital post, I am also wondering if the the OP was also asking How to leave a tip, as well as how much. We forget that if you live somewhere where people tip, we've grown up observing it and it's procedures.

Let's assume we are talking about the U.S., where tipping is the norm. The way to give tips may/will be different in other cultures/countries.
I can think of times the person unfamiliar may be confused as in "why did you give a tip here, but not there?"

For starters

Restaurants/food vendors
If you are in a place where you sit down, someone takes your order, comes back with your food/drinks, you tip. At the end of the meal, you would get the servers attention and say "Check please" The bill for your food in this case is called a check.
Regardless of whether you are paying with a credit card or with cash, I try to always leave the tip in cash. On the credit card receipt there will be a line that says "Tip". I always draw a line through that, and in the Total line below it write in what the total of the bill was, then sign the credit card reciept. The server will come back, take your signed receipt, and then come back again with your copy. Then, as I am leaving, I will take the money I am going to leave as a tip and leave it on the table, ususally holding a corner of it down with a glass, the salt shaker, etc.
Don't worry, no one else is going to come along and take that money. It's understood that is for the server.

The reason for leaving the tip in cash is because if you add it to the credit card, the server will be fully taxed for it. I will put it on a credit card sometimes, but only if I just don't have any cash on me.

When traveling, or for anyone really, it's a good practice to carry around some cash, in small denominations, like $1, $5, to leave or give as tips. I always try to make sure I have at least five $1 bills, and one or two $5 bills on me, that's reserved for tipping when the occassion arises.

If you are paying cash for the meal, when the server brings check to you, if you have the cash that would equal what the meal cost, plus what you will leave as a tip, just give the server all that saying "keep the change" or "the rest is for you" They will say "Thank you" and that's it.

Let's say though that you don't have close to the exact amount you want to leave. Then, you would give the server a $10 or $20 bill and say "Could you please bring me change for this, with 5 singles?" The server understands you are making change to leave a tip.
However, I always make sure I mention to bring singles, because I've had servers come back with change for a $20 with no singles, and this is annoying, and more important, makes me feel like the server is trying to get you to leave more of a tip than you wanted. This in itself is a sign of a bad server.
If they do this, don't feel shy about saying "I need singles".

When leaving a tip, round to the nearest dollar. When in doubt round up. It's really not usual to leave coins as part of a tip.

Next - restaurants that you walk into, order food from a counter, you pay for it and get the food, and leave or go sit at a table and eat.
If it's a fast food restaurant, you don't leave any sort of tip.

If you go order at a counter, get your food, but you see someone who works there is cleaning up the tables after customers leave, it's a nice thing to leave a dollar.
If you order at a counter, but someone brings your food over, and checks on you during your meal to see if you need anything, and cleans your table, leave 10%, or a least a dollar.

Some places have a "tip jar" on the counter by the register. You are free to put in the coins of your change, or a dollar, or nothing. You won't be treated any differently.

It's important to remember that the person serving you at a restaurant is your equal, and treat and talk to them accordingly. Don't speak to them as if they are beneath you, or treat them badly.
Leave your tip based on their performance on how well they took care of you, and don't penalize them for something beyond their control.
It's not their fault if you don't like the taste of your food. If a restaurant is very busy, and you can see they are working hard and doing their best, don't leave them less of a tip because you had to wait.

Keep in mind that you are traveling abroad to have a good time, learn new things, like seeing how others live.
Don't be such a penny pincher that you can't even leave a decent tip at a restaurant.
Personally, I would never leave 10%, unless it was a situation mentioned above.

You'll find differing opinions, but for me, I think if you can't afford to leave a decent tip, you should have just stayed home.

Now, please be aware that food servers in the U.S. have a very low wage, earn most of their money on tips. I know it's not like that in other countries, but that's a totally different topic for a different thread.
I'm talking about how it is right now, today.

There are other situations for tipping. I've just covered when you are going out to eat. But this is good for a start.

OH! If you are having food delivered to you, tip the delivery driver, tip 15% of the bill, or at least a dollar or two if a small order.

It's just an excuse to force folk to live on the breadline - Enforce a minimum wage and tipping becomes gratuitous, not an 'expectation'.
You simply promote poverty otherwise.

You're not finding an argument here.

However, this person, from China, asked how to tip appropriately in America.

I'm answering that.

When traveling in a taxi, a tip is expected. About 15%. I looked it up, and if they help you with your suitcases or large bags, give them an extra dollar or two.

I've never used Uber, or other similar transportation, so I had to look this part up.
Uber drivers keep 80% of their fare (what the customer pays) and pays Uber the other 20%. So, while it's not necessary to tip, I'm sure it's welcome.

I saw this picture below, where someone as devised a tip box that doubles as a cell phone charging station. I like that idea. Charge your device, leave a dollar or two. It's a nice way to handle it.

Whether that is true or not is moot.

If you don't tip you are screwing the server.

Many people here in the US agree that instead waitstaff should be given a higher wage, however, that is not the way it is. Not tipping is not going to change that - changing the law of minimum wage for waitstaff will change this.

The OP is a caring person obviously that is considerate and wants to do what is appropriate. Nice to see people being considerate of different cultures.

This.

One other thing to add - just to make things more complex - some restaurants will add the tip onto the bill. For example if there is a large party usually this is noted on the menu or elsewhere ---- for parties of 8 or larger an 18% gratuity will be added to the bill. I have even seen some places that have many tourists also add the gratuity to the bill to "protect" their servers from travelers that have different custom (ie Mark Noble).

Just double check your bill/check as it should itemize all charges including if a tip is added - this is not the norm but does sometimes happen.

You're absolutely right , but it's become part of North American culture. There are some restaurateurs who are trying to change the practice but there have been complaints about that as well.

If you travel to North America and eat out you are stuck with tipping unless you go to one of the few restaurants that have increased salaries and banned tipping.

Since you've already said you can't afford to eat out, it seems unlikely that you'll be travelling to North America in the short term, so it's not a problem for you.