You need about 8–7.5 regular water bottles to make a gallon , depending on which “regular” size you mean.

Quick Scoop

  • 1 U.S. gallon = 128 fluid ounces (fl oz).
  • Common bottle sizes and how many make 1 gallon:
* 8 oz bottles → **16 bottles** per gallon
* 12 oz bottles → **about 10.7 bottles** per gallon
* 16 oz bottles → **8 bottles** per gallon

* 16.9 oz “500 ml” bottles → **about 7.5–7.6 bottles** per gallon

* 20 oz bottles → **about 6.4 bottles** per gallon

* 24 oz bottles → **about 5.3 bottles** per gallon

The simple formula

To figure it out for any bottle size:

Number of bottles=128ounces per bottle\text{Number of bottles}=\frac{128}{\text{ounces per bottle}}Number of bottles=ounces per bottle128​

You just divide 128 (ounces in a gallon) by the size of your bottle in ounces.

Example: If your bottle is 16.9 oz:
128 ÷ 16.9 ≈ 7.57 → so about 7½ standard 16.9 oz bottles make a gallon.

One-line takeaway

If you’re using typical small store-bought bottles (16–17 oz), count 7–8 bottles to be roughly a gallon of water.

TL;DR:

  • 1 gallon = 128 oz.
  • Standard 16.9 oz bottle → ≈ 7.5 bottles per gallon.

Information gathered from public forums or data available on the internet and portrayed here.