# Dewpoint calculation possible? **URL:** \ **Category:** Questions & Help\ **Created:** [March 26, 2019, 12:20pm UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039 "2019-03-26T12:20:15Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Osorkon](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/osorkon/32/43026_2.png) [@Osorkon](https://community.homey.app/u/Osorkon)\ **Post date:** [March 26, 2019, 12:20pm UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/1 "2019-03-26T12:20:15Z")
Is there a way to calculate the Dewpoint using a temperature and humidity Sensor? Can I do it with the logic app? Or maybe there is a another App I can handle a komplex formula? Thanks an greeting Osorkon ---
**Author:** ![KonradWalsh](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/konradwalsh/32/147_2.png) [@KonradWalsh](https://community.homey.app/u/KonradWalsh)\ **Post date:** [March 26, 2019, 12:25pm UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/2 "2019-03-26T12:25:45Z")
> [@Osorkon](#): > > calculate the Dewpoint Yes Create a Logic Variable or Better Logic Variable Use a flow to set a calculation card with `((T - ((100 - RH)/5))` T = Temp in Celsius RH = Relative Humidity ---
**Author:** ![Osorkon](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/osorkon/32/43026_2.png) [@Osorkon](https://community.homey.app/u/Osorkon)\ **Post date:** [March 26, 2019, 2:00pm UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/3 "2019-03-26T14:00:05Z")
Unfortunately the dew point calculation is not a linear function! Your formula is too rough. I have several degrees difference! The formula only returns the correct dew point with T=21 and RH=60! I see your formula for the first time. If it would be so easy, I would not have searched here for advice! I would like to use this formula. ![image](https://us1.discourse-cdn.com/flex025/uploads/athom/original/2X/c/cb67f3c2dad510cacfcae1a4b65deb564f5caf39.png) I’m either too stupid or it doesn’t work with better logic?! ---
**Author:** ![KonradWalsh](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/konradwalsh/32/147_2.png) [@KonradWalsh](https://community.homey.app/u/KonradWalsh)\ **Post date:** [March 26, 2019, 2:15pm UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/4 "2019-03-26T14:15:56Z")
Your welcome ---
**Author:** ![Ton\_Meek](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/ton_meek/32/149_2.png) [@Ton\_Meek](https://community.homey.app/u/Ton_Meek)\ **Post date:** [March 26, 2019, 3:34pm UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/5 "2019-03-26T15:34:32Z")
Arh = {{log(Luchtvochtigheid/100)+(17.62\*Temperatuur/(243.12+Temperatuur))}} en Tdauw = {{round(243.12\*Arh/(17.62-Arh),2)}} Arh is een hulpvariabele en de formules kunnen in Logica van Homey. Vergeet de accolades niet. Je kunt meer info vinden op [Weerschip](http://www.weerschip.nl/formules.html) Sorry, that I replied in Dutch. ---
**Author:** ![Osorkon](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/osorkon/32/43026_2.png) [@Osorkon](https://community.homey.app/u/Osorkon)\ **Post date:** [March 26, 2019, 6:31pm UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/6 "2019-03-26T18:31:24Z")
Thanks a lot @Ton_Meek ! It works perfectly Now there is nothing in the way for my dew-point aeration project! 😀 ---
**Author:** ![jeroenvano](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/jeroenvano/32/721_2.png) [@jeroenvano](https://community.homey.app/u/jeroenvano)\ **Post date:** [March 27, 2019, 6:29am UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/7 "2019-03-27T06:29:51Z")
Just curious, in what scenario would you use the dewpoint as a trigger? ---
**Author:** ![Osorkon](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/osorkon/32/43026_2.png) [@Osorkon](https://community.homey.app/u/Osorkon)\ **Post date:** [March 27, 2019, 7:14am UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/8 "2019-03-27T07:14:30Z")
I use the dew point for ventilation control. Or the difference of dew point inside and outside. Especially in summer for targeted reduction of humidity in rooms. If the dew point outside is lower than the dew point Indoor = Ventilation is recommended. Currently I get the ventilation recommendation visualized when opening a window via an LED strip! Red = do not recommend airing Green = airing allowed Later, I wanted to invest in decentralized ventilation and automatically control it in conjunction with a dehumidifier. ---
**Author:** ![jeroenvano](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/jeroenvano/32/721_2.png) [@jeroenvano](https://community.homey.app/u/jeroenvano)\ **Post date:** [March 27, 2019, 8:01am UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/9 "2019-03-27T08:01:28Z")
Nice use case thanks for sharing 😀 ---
**Author:** ![Marcel\_Wolf](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/marcel_wolf/32/8087_2.png) [@Marcel\_Wolf](https://community.homey.app/u/Marcel_Wolf)\ **Post date:** [March 27, 2019, 10:57am UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/10 "2019-03-27T10:57:39Z")
Can someone explain how to use the logics variable. I only get formulas instead of values. ![Knipsel](https://us1.discourse-cdn.com/flex025/uploads/athom/original/2X/4/418f9b8555be87f54683f4f6b193660f9446d1ef.png) ---
**Author:** ![Osorkon](https://sea1.discourse-cdn.com/flex025/user_avatar/community.homey.app/osorkon/32/43026_2.png) [@Osorkon](https://community.homey.app/u/Osorkon)\ **Post date:** [March 27, 2019, 11:10am UTC](https://community.homey.app/t/dewpoint-calculation-possible/11039/11 "2019-03-27T11:10:36Z")
Like this: ![image](https://us1.discourse-cdn.com/flex025/uploads/athom/original/2X/5/55ed54d0f383dfc62b60c504352fca4e36359198.jpeg) ![image](https://us1.discourse-cdn.com/flex025/uploads/athom/original/2X/c/cd3a696dceb8d8804c29a4ac110f72fa67b45df5.jpeg) That’s the result: ![image](https://us1.discourse-cdn.com/flex025/uploads/athom/original/2X/6/6bbe86cfbac5e40f9df9897a8f9058022a040975.jpeg)