In small quantities, grams and mls are similar.

Gels

A gel is made from water and a thickening agent, eg, xanthan gum, hydroxyethylcellulose.

Basic gel with xanthan gum

200g water
5g xanthan gum

Sprinkle the xanthan gum (which is a powder) over the water, whisking vigorously. Blend until smooth with electric blender making sure you ease out all the lumps.
So that's your gel!

Add:
2d preservative (This is essential. The gel with go mouldy within days without it.)

Other alternatives:
5g essential oil of choice
5g glycerin
1g organic aloe vera powder  to the water for organic aloe vera gel.

Basic organic gel with Emulsifier O

(This makes a white gel with an unusual foamy texture. It makes quite a nice lotion.)
200g water
10g Emulsifier O
Preservative as directed

Heat both the above separately to 75 deg C, combine and blend on and off with a stick blender until 40 deg C.

Add other ingredients:
5g essential oil
5g glycerin
1g aloe vera powder (add this to the water at the beginning)
5g hydrolysed wheat protein