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Some bike shops have gel pads that you sit on to measure the distance between your sit bones. Is it possible to take this measurement on your own at home, or does this really require special-purpose equipment?

[Related question: Should I use a narrower saddle on a road bike than I would on my hybrid commuter?]

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I came across another suggestion, which I'll include for completeness: sitting on a ziploc bag containing flour. –  amcnabb Jun 19 '12 at 23:17
    
This only works with a very strong bag or a very light rider. Not something my wife would be happy about me trying. :) –  zenbike Sep 9 '12 at 2:57
    
Another suggestion I saw was to use aluminum foil over a towel. –  amcnabb Sep 11 '12 at 3:52
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5 Answers

up vote 10 down vote accepted

Copied this from a saddle mfg website: How to measure your own sit bones

Of course the measure you really want is between the centres of your ischial tuberosities – the pointy lower parts of your pelvic bone on either side. Many bike dealers have a pad that you can sit on to measure this distance, but you can do it at home too.

Take a piece of aluminium kitchen foil and place it on a carpeted stair. Sit on the foil, lean forward a bit to approximate your riding position, then lift your feet. This should leave a good impression of your rear in the foil, and you can measure between the two points of deepest impression to get your sit bone width.

‘Narrow’ sit bone width would be 100mm or less, medium 100-130mm, wide over 130mm.

A saddle’s width is measured from edge to edge across the top, and Specialized recommends a 130mm saddle width for narrow, 143mm for medium and 155mm for wide. These figures should translate approximately across other ranges, with all other factors taken into account.

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Here's a link to a video that may help you:

In this technique all you need is a piece of corrugated cardboard and some chalk.

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I've used this method which worked well:

  1. Fill a large size ziploc bag with icing sugar. Icing sugar's fine texture means that it binds together when compressed. This is what we want - it will hold the shape of your buttprint after you get up.

  2. Close the bag making sure to squeeze out the air.

  3. Place on hard chair.

  4. Sit while assuming the degree of forward rotation that you intend to cycle with. The distance between your sit bones change depending on this rotation.

  5. Get up cleanly and measure the distance between the depressions.

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Sweet! (What else can I say?) –  Daniel R Hicks Sep 1 '13 at 12:55
    
I can see some explaining to the wife if you don't get all the air out......There has to be a sitcom episode in this idea...... –  mattnz Sep 2 '13 at 6:50
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A fresh piece of corrugated cardboard on a hard surface such as a coffee table. Sit down and try to mimic the upper body position you have on your bike. Your sit bones change position based on how your pelvis is tilted. Your sit bones should crush the corrugated cardboard slightly and leave two indentations. Measure center to center as best you can.

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You can't mimic your riding position, and get an impression of your sit bones. Using the position with your knees 4-6 inches above the impression material matches the method that manufacturers are using to get data to build their saddles, and is thus the most likely to match with the recommendations available on the market. –  zenbike Sep 9 '12 at 2:55
    
I should have quantified that my coffee table, if it were a bike, would be categorized as a low rider... –  802bikeguy.com Sep 18 '12 at 4:10
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Wouldn't it make more sense to do this on a bike? –  Neil Fein Dec 2 '12 at 19:52
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@NeilFein That's a catch 22. You're assuming the saddle on your bike will hit your sit bones correctly, in which case this whole exercise is redundant. –  meagar May 27 '13 at 18:08
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You can do it on any surface which will conform to the shape of your butt, like a piece of memory foam.

Sit on it, with your knees higher than your seat by 4-6 inches, then measure the center of the depressions left.

There are different types of memory foam, and some will have a more durable impression than others.

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I recently found a page (specialized.custhelp.com/app/answers/detail/a_id/1181/~/…) on Specialized's customer service site that gives this basic advice and adds a suggestion to use ball bearings to find the center of each indentation. –  amcnabb Sep 9 '12 at 2:36
    
That is actually quite brilliant. I like it. –  zenbike Sep 9 '12 at 2:56
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