How do I weigh this giant box?
November 4, 2013 10:45 PM   Subscribe

I have a large road case (2.5 / 2.5 / 3 feet) that I need to weigh. It is too big to fit on one scale. Would it work to place one scale under each of the 4 wheels and average the 4 weight readings? My physics-fu is not strong enough to figure this one out on my own. Help!
posted by TheCoug to Science & Nature (13 answers total)
Is it light enough that you can hold it? In situations like these I normally weigh myself without the case then pick it up and weigh myself while holding the case. Find the difference and you've got the weight of the case!
posted by schmoo at 10:56 PM on November 4, 2013 [1 favorite]

Actually, sorry - looking at the dimensions it looks like no matter how light it is, it would be too large to hold. Woops!
posted by schmoo at 10:57 PM on November 4, 2013

Are you trying to weigh it for shipping?

If you are then just a estimated guess will be fine. If there is too much of a difference between your guess and the real weight the shipping company will either let it go or automatically adjust your charge.
posted by manderin at 10:57 PM on November 4, 2013

Best answer: Yes, you can, and you can even improve on it, and do it with just 1 scale.

Use spacers under 3 wheels and the scale under a fourth, and record the weight for the wheel with the scale under it. Rearrange until you have weighed all 4 wheels in the same fashion, and *add* the 4 weights to obtain the weight of the case.

The spacers should be as close as possible to the height of the scale when it is under load. Make sure that the spacers are all the same height, and make sure you perform the experiments on a level floor.
posted by the Real Dan at 11:20 PM on November 4, 2013 [2 favorites]

Is there some smaller, sturdy, flattish object you could place on the scale first to act as a spacer, then carefully center the box on top of? I'm picturing a large dictionary or metro area phone book.
posted by Dixon Ticonderoga at 11:21 PM on November 4, 2013 [1 favorite]

Balance the case on one corner or edge?
posted by sebastienbailard at 11:46 PM on November 4, 2013

Best answer: if you have 4 scales and can place one under each wheel, then you need to add rather than average the readings (since the weight is being distributed across all the scales instead of just one).
posted by russm at 11:55 PM on November 4, 2013

Response by poster: Thanks folks!
posted by TheCoug at 12:11 AM on November 5, 2013

You don't need four scales; just put two under diagonally opposite wheels, then balance the case on them by pushing horizontally on the edge that still has its wheel on the ground. Or if that doesn't quite work, put a third scale under that wheel.
posted by nicwolff at 1:55 AM on November 5, 2013

Adding weights from multiple scales works just fine. It's a trick well known to fat men like me since the advent of digital bathroom scales which, unlike the old spring dial types, display an overload indicator above their maximum rated load rather than simply wrapping around and letting me subtract 130kg from whatever the dial says.

There is no need to try to spread the weights evenly across your multiple scales. As long as no part of the object is touching anything but a scale, and the scale readings are stable, they're always going to sum to the total weight of the object.

If your object is not fully supported by your scales - that is, if some part of it is still resting on the ground, or you're applying sideways force by hand to prevent some part of it falling to the ground - you won't get an accurate weighing.
posted by flabdablet at 2:48 AM on November 5, 2013

A simpler method might be to find a corrugated cardboard box that fits on the scale and will still support the weight of the road case after you've cut away enough of one side to see the scale's display while the road case is balanced on top of the box. Cardboard boxes weigh close enough to nothing to make the reading accurate enough for all practical purposes.
posted by flabdablet at 2:52 AM on November 5, 2013

Your local Veterinarian has a scale for stuff like this It will take 10 seconds. Bring baked goods.
posted by timsteil at 9:32 AM on November 5, 2013

  1. Weigh yourself.
  2. Pick up case.
  3. Balance case on head, using hands to steady it.
  4. Subtract your weight from weight of you plus case.
  5. Job done.

posted by Scientist at 10:38 AM on November 5, 2013

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