What should I put as my household size on when I file my 1040 federal tax return?

Your tax return does not ask for household size. Since she can claim you as a dependent, she can also file as Head of Household if she's otherwise eligible. You can't file as HoH since you don't have a qualifying person living in your home (such as your child or a parent that you support) and you don't pay more than half of the cost of maintaining the home. Since you can be claimed as a dependent you can't claim dependents anyway, so HoH status for you is absolutely off the table.

Among other requirements, you must have a closely related dependent to file as head of household. So you are NOT HofH whether you're a dependent or not. From your description though, sounds like you ARE a dependent of your grandmother. Your tax return doesn't ASK for household size, so don't know what you're talking about there. If you're talking about your W-4, if you're a dependent you should put single/zero allowances.

you are definitely NOT head of household a qualifying child is one who is not yet 24, attends full time school 5 months of the year, lives in the household of parents(guardian--g'mother is a parent) 6 months of the year and the parent provides more than 50% of the support of the child you may pay her something along the way but it may be necessary for you to prove you are providing more than 50% of your support in contrast to how much she pays support is considered rent(mortgage), utilities, home phone, food, clothing, medical, entertainment and transportation(not car insurance)

You would have a household size of one. Because your grandmother is paying for most of your care, she might be able to claim you as part of her household, but not the other way around. If you were the majority caregiver for your grandmother whether she lived with you or not, you might be able to claim some benefit for those expenses on your taxes, but that is not the current situation for you.

You need to check the tax rules for head of household filing status- I don't believe that you are eligible for the status since you do not have a "qualifying person"- which is generally a child/dependent of yours. Also your grandmother may be able to claim you as a dependent- this does not mean that she has to, but across both of the tax returns only one person can. If you meet the requirements of being a dependent- she provides for more than 50% of your care- including housing, food etc. then she can. You may want to talk about it together and determine which filing will get you both the most benefit and then hash out who gets what amount of the related tax break.

Among other requirements, you must have a closely related dependent to file as head of household. So you are NOT HofH whether you're a dependent or not. From your description though, sounds like you ARE a dependent of your grandmother. Your tax return doesn't ASK for household size, so don't know what you're talking about there. If you're talking about your W-4, if you're a dependent you should put single/zero allowances.

You need to check the tax rules for head of household filing status- I don't believe that you are eligible for the status since you do not have a "qualifying person"- which is generally a child/dependent of yours. Also your grandmother may be able to claim you as a dependent- this does not mean that she has to, but across both of the tax returns only one person can. If you meet the requirements of being a dependent- she provides for more than 50% of your care- including housing, food etc. then she can. You may want to talk about it together and determine which filing will get you both the most benefit and then hash out who gets what amount of the related tax break.

You would have a household size of one. Because your grandmother is paying for most of your care, she might be able to claim you as part of her household, but not the other way around. If you were the majority caregiver for your grandmother whether she lived with you or not, you might be able to claim some benefit for those expenses on your taxes, but that is not the current situation for you.

you are definitely NOT head of household a qualifying child is one who is not yet 24, attends full time school 5 months of the year, lives in the household of parents(guardian--g'mother is a parent) 6 months of the year and the parent provides more than 50% of the support of the child you may pay her something along the way but it may be necessary for you to prove you are providing more than 50% of your support in contrast to how much she pays support is considered rent(mortgage), utilities, home phone, food, clothing, medical, entertainment and transportation(not car insurance)