# About the Volume of the required media
**URL:** https://www.evolver.bio/t/about-the-volume-of-the-required-media/330
**Category:** Experiments
**Created:** [December 9, 2021, 2:33pm UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330 "2021-12-09T14:33:30Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@sunachi](https://www.evolver.bio/u/sunachi)
#### Post date: [December 9, 2021, 2:33pm UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330/1 "2021-12-09T14:33:30Z")
Hi, eVOLVER experts
I am now setting some experiments, and found that I need 25 L for almost 5 days experiments ! (20 mL for culture volumes, 1.5 h for Avg.doubleing time, 16 for the number of cultures)
I calculated the required media by using the metrics in the Supplementary Notes 8 below.
Because it’s my first time with continuous culture, it is just surprising me.
Is 25 L for 5 days kind of normal volumes often used ??
Thank you very much for your help!
Best wished
---
### Author:  [@danigarcia](https://www.evolver.bio/u/danigarcia)
#### Post date: [December 10, 2021, 10:45am UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330/2 "2021-12-10T10:45:19Z")
Hi @sunachi,
If you are running a turbidostat, the media consumption will also depend on the cell density range you will be using e.g. for a lower\_thres = 0.1 and higher\_thres = 0.8, cells are growing for 3 generations without a dilution, so you will use a bit less medium.
I use the following formula to calculate my eVOLVER’s consumption:
**experiment\_time** / _time\_between\_dilutions_ \* **volume\_per\_dilution**
which extends to the following:
**days \* 24** / _( LOG2 ( upper / lower ) \* gtime )_ \* **( 1 - lower / upper ) \* volume**
You can also use [this excel sheet](https://github.com/dgruano/evolver-utils/blob/main/eVOLVER%20Consumption.xlsx).
Hope it helps!
Dani
---
### Author:  [@sunachi](https://www.evolver.bio/u/sunachi)
#### Post date: [December 18, 2021, 4:45am UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330/3 "2021-12-18T04:45:30Z")
@danigarcia Thanks for the tips!!
By the way, what is **gtime** in your extended formula ?
Bests,
sunachi
---
### Author:  [@danigarcia](https://www.evolver.bio/u/danigarcia)
#### Post date: [December 20, 2021, 9:14am UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330/4 "2021-12-20T09:14:01Z")
Generation time, so the same as doubling time in the formula from the paper.
---
### Author:  [@sunachi](https://www.evolver.bio/u/sunachi)
#### Post date: [March 10, 2023, 5:13pm UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330/5 "2023-03-10T17:13:26Z")
Hi @danigarcia ,
It’s been a while since this post, but I’m thinking about it again.
In turbidostat in custom\_script.py, the code is
`-np.log e (lower_thres / Ave.OD) * volume / flow_rate`
so, this means that required volume per dilution is
① `-np.log e (lower_thres / Ave.OD) * volume`
but in your reply above, it says
② `( 1 - lower / upper ) * volume`
Which is more accurate for calculating the required volume per dilution, 1 or 2??
In my setups, the original code (i.e., ①) seems to work well, though.
Thanks!
sunachi
---
### Author:  [@danigarcia](https://www.evolver.bio/u/danigarcia)
#### Post date: [June 7, 2023, 8:27am UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330/6 "2023-06-07T08:27:07Z")
Hi @sunachi,
After giving it a thought, I believe the first one is the most accurate. While my approach is a linear approximation (it assumes we first remove the culture volume and then we add the fresh medium), the dilution follows an exponential, since the input and output run at the same time, so ① should be the most accurate!
Cheers!
---
### Author:  [@sunachi](https://www.evolver.bio/u/sunachi)
#### Post date: [June 11, 2023, 1:03pm UTC](https://www.evolver.bio/t/about-the-volume-of-the-required-media/330/7 "2023-06-11T13:03:15Z")
Hey Dani,
Thank you very much!