How much blood is that?

An adult carries about five litres of blood. Losing a fifth of it is survivable; losing two fifths usually is not.

The volume Unit

Almost exactly UK blood donation

470 mL is bigger than 2 of the 7 references on this page.

Reference figures are measurements and are rounded; the unit conversion behind them is exact.

Every reference on this page, with its size and its ratio to your number
Reference	Size	Yours ÷ theirs	Note
blood test vial	5 mL	94×
nosebleed	20 mL	23.5×
UK blood donation	470 mL	1×	470 ml, about 8% of your blood
US blood donation	500 mL	0.94×
class 1 blood loss	750 mL	0.627×	Up to 15% — no symptoms
class 3 blood loss	2,000 mL	0.235×	30–40% — shock
total adult blood volume	5,000 mL	1/10.6	About 5 litres

A UK donation takes 470 ml, about 8% of an adult’s blood, and the plasma is replaced within 24 hours. Red cells take six weeks.
Blood volume is roughly 70 ml per kilogram of body weight, so a 70 kg adult carries about 4.9 litres.

Frequently asked

About 4.5 to 5.7 litres in an adult, or roughly 7% of body weight. Children have proportionally more per kilogram.

Up to about 15% causes no symptoms — a blood donation is well inside that. Beyond 30% causes shock and needs urgent replacement.

These are population figures for orientation, not clinical guidance.