# Density of water question

**URL:** <https://boards.straightdope.com/t/density-of-water-question/201060>\
**Category:** Factual Questions\
**Created:** [September 11, 2003, 10:17pm UTC](https://boards.straightdope.com/t/density-of-water-question/201060 "2003-09-11T22:17:39Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Mailbox](https://avatars.discourse-cdn.com/v4/letter/m/7feea3/32.png) [@Mailbox](https://boards.straightdope.com/u/Mailbox)\
**Post date:** [September 11, 2003, 10:17pm UTC](https://boards.straightdope.com/t/density-of-water-question/201060/1 "2003-09-11T22:17:39Z")

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Is there temperature at which the density of water ice is lower than that of 4°C liquid water? I’m assuming that the 4°C is the point at which it is typically said that water is most dense. Assuming standard pressure as well.

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**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\
**Post date:** [September 11, 2003, 10:20pm UTC](https://boards.straightdope.com/t/density-of-water-question/201060/2 "2003-09-11T22:20:39Z")

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I’m not sure I understand the question. Water ice is _always_ less dense than liquid water of any temperature. Liquid water at 4 [sup]o[/sup] C is at it’s most dense, but still more dense than solid ice.

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**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\
**Post date:** [September 11, 2003, 10:49pm UTC](https://boards.straightdope.com/t/density-of-water-question/201060/3 "2003-09-11T22:49:37Z")

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[Here’s a nice table](http://www.lsbu.ac.uk/water/phase.html) giving the density of 17 different forms of water ice. Ice X and XI have the highest density, at ~2.51 g/cm[sup]3[/sup].

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**Author:** ![refusal](https://avatars.discourse-cdn.com/v4/letter/r/ac91a4/32.png) [@refusal](https://boards.straightdope.com/u/refusal)\
**Post date:** [September 12, 2003, 12:14pm UTC](https://boards.straightdope.com/t/density-of-water-question/201060/4 "2003-09-12T12:14:59Z")

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Does the OP mean, is there a temperature at which the density of ice is **higher** than that of water at 4 C?

Since most solids contract as they cool and hence get denser (just as they expand when heated), if you cool ice sufficiently would it contract to be more dense than water at 4 C?

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**Author:** ![zut](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zut/32/2875_2.png) [@zut](https://boards.straightdope.com/u/zut)\
**Post date:** [September 12, 2003, 12:50pm UTC](https://boards.straightdope.com/t/density-of-water-question/201060/5 "2003-09-12T12:50:01Z")

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I think the answer to that is no. The coefficient of thermal expansion of ice is [50 X 10[sup]-6[/sup]/[sup]o[/sup]C](http://www.its.caltech.edu/~atomic/snowcrystals/ice/ice.htm). The density of ice at 0[sup]o[/sup]C is 917 g/cc, while the density of water at 4[sup]o[/sup]C is 1000 g/cc. Assuming the COTE is constant, that implies that the density of ice at 0K is 917\*[1/(1 + 50X10[sup]-6[/sup]\*273)[sup]3[/sup]] = 955 g/cc.

However, the table **Squink** links to says that ice undergoes a phase change from Ice I to Ice XI at about 75K, which would increase density quite a bit. Does it really do that?