• Question: if you hv less blud do u weigh less tell me the truth

    Asked by saff to Dalya, Derek, Sarah, Tim, Tom on 14 Jun 2011.
    • Photo: Tim Millar

      Tim Millar answered on 14 Jun 2011:

      Lets do the maths then. If I weighed you and you came out about 50kg, then removed a litre of blood which will weigh around 1kg, then yes you should weigh less.

      However, we are making new blood cells all the time so we would need to be quick and have accurate ways to measure you so that we could see the difference. Much of that litre is also water, so we would have to stop you from having anything to drink between taking the blood and measuring you.

    • Photo: Dalya Soond

      Dalya Soond answered on 14 Jun 2011:

      Of course you would weigh less, you would be removing part of your weight.

      The average adult has between 4.5-5 litres of blood and blood weighs 1.05 times as much as water (because it has ocells and molecules in it that weigh more than water). So if you donated 10% of your blood (about 500 Litres) which is a generous thing to do when you are old enough, you would loss about 525 grams -or about 1.15 pounds.

      However, blood regenerates very quickly. You would replace most parts of this blood within the next 2 days.

    • Photo: Sarah Thomas

      Sarah Thomas answered on 14 Jun 2011:

      Yes, you weigh less after you give blood. I give blood 3 times a year and weigh myself every wednesday (and I would like to say that the reason I weigh myself every wednesday is because I weigh my puppy every wednesday but he is too big for the scales so I have to pick him up, weigh us combined, then put him down and substract our weights!!) and yes I weighed less after giving blood one time but the next week I was back to normal again. After you give blood the nurses get you to drink lots and eat chocolate biscuits!!

    • Photo: Tom Crick

      Tom Crick answered on 14 Jun 2011:

      Yes definitely — we can reasonable precise about how much:

      The average density of blood is 1060 kg/m^3…

      1m^3 = 1000ml

      Thus blood weighs around 1.06kg/l — this means that if you remove a litre of blood, you will lose around 1kg.

    • Photo: Derek McKay-Bukowski

      Derek McKay-Bukowski answered on 14 Jun 2011:

      Well, the biologists have already answered this one pretty well. However, I’ll reinforce Tim’s point that your food and drink has weight too. So, if you donate 1 pint of blood and then drank a 1 pint of orange-&-lemonade, then your weight is barely going to change at all.

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