You need to weigh at least 110 pounds (50 kilograms) to donate blood in the United States. This is the standard minimum for whole blood, platelet, and plasma donations, and it’s set by the FDA as a federal regulation. If you’re younger than 19, the rules get more specific, factoring in your height as well.
The 110-Pound Rule and Why It Exists
A standard whole blood donation draws about one pint (roughly 470 mL) of blood. Your body’s total blood volume is closely tied to your weight. Someone who weighs 110 pounds has approximately 3,500 mL of blood, so donating one pint removes about 13% of their total supply. That’s a safe margin. Drop much below 110 pounds and that same pint starts to represent a larger percentage of total blood volume, which increases the risk of fainting or feeling lightheaded during or after donation.
UK transfusion guidelines specify that a donation should never exceed 16% of a donor’s estimated blood volume, and that young women in particular face a significant risk of fainting when the donation exceeds 15%. The 110-pound cutoff keeps most donors well within those safety thresholds.
Requirements for Donors 18 and Younger
If you’re 18 or younger, the minimum weight often depends on your height. Shorter donors need to weigh more to have enough blood volume for a safe donation. These height-weight charts vary slightly between blood centers, but Stanford Blood Center’s guidelines are a good example of the general pattern.
For male donors 18 or younger:
- 5’0″ or taller: at least 110 lbs
- 4’11”: at least 114 lbs
- 4’10”: at least 118 lbs
- 4’9″: at least 123 lbs
- 4’8″: at least 126 lbs
- 4’7″ or shorter: at least 130 lbs
For female and nonbinary donors 18 or younger:
- 5’6″ or taller: at least 110 lbs
- 5’5″: at least 115 lbs
- 5’4″: at least 120 lbs
- 5’3″: at least 124 lbs
- 5’2″: at least 129 lbs
- 5’1″ or shorter: at least 133 lbs
The difference between male and female charts reflects biological differences in blood volume. On average, females carry less blood per pound of body weight than males, so a shorter female donor needs to weigh more to have the same safe margin. Once you’re 19 or older, most blood centers use the flat 110-pound minimum regardless of height or sex.
Power Red Donations Have Higher Thresholds
A Power Red (double red cell) donation takes twice the usual amount of red blood cells while returning plasma and platelets to your body. Because it removes more red cells, the weight and height requirements are stricter.
- Male donors: at least 5’1″ and 130 lbs
- Female donors: at least 5’3″ and 150 lbs
Standard whole blood, platelet, and plasma donations all share the same 110-pound minimum. Power Red is the only common donation type with a higher bar.
What Happens if You’re Close to the Minimum
If you weigh right around 110 pounds, you’re still eligible, but you’re giving up a slightly larger share of your blood volume than a heavier donor. Research on donor reactions confirms that low body weight is a well-established risk factor for vasovagal reactions, the medical term for the lightheadedness, dizziness, or fainting that can happen during or after donation. One study found that “at risk” donors (younger and lighter) experienced vasovagal reactions at about twice the rate of the general donor population: 2.0% compared to 0.96%.
That said, the overall risk is still low. And while lighter donors may be slightly more likely to feel faint, the weight itself doesn’t predict how severe the reaction will be. Eating a solid meal, drinking plenty of water in the hours before your appointment, and avoiding standing up quickly afterward all help reduce the chance of a reaction regardless of your weight.
How Requirements Compare Outside the U.S.
The U.S. minimum of 110 pounds (50 kg) is on the lower end internationally. The UK’s NHS requires donors to weigh between 50 kg (110 lbs) and 158 kg (about 348 lbs), setting both a floor and a ceiling. Women under 20 in the UK face additional screening if they weigh under 65 kg (143 lbs) or stand shorter than 5’6″, reflecting the same blood-volume concerns that drive the U.S. height-weight charts for younger donors.
If you’re donating while traveling or at a center run by a different organization, it’s worth checking their specific requirements. The 110-pound minimum is nearly universal in the U.S., but the details around younger donors and specialty donations can vary from one blood center to the next.