The french phrase faire le plein de is a common and useful expression. It literally means to fill up, but it has several figurative meanings.

The core meaning: filling a tank

The most basic use of faire le plein is for filling the fuel tank of a vehicle.

• Je dois faire le plein avant de prendre l’autoroute.
  I have to fill up before taking the highway.
• Faites le plein, s’il vous plaît.
  Fill it up, please.
• Le prix pour faire le plein a beaucoup augmenté.
  The price to fill up the tank has gone up a lot.

In this context, you will often hear the noun plein used alone.

• Un plein d’essence, s’il vous plaît.
  A full tank of gas, please.

Figurative use: stocking up

You use faire le plein de to talk about getting a large quantity of something you need. It is like stocking up.

• Il faut faire le plein de provisions pour le weekend.
  We need to stock up on supplies for the weekend.
• Nous faisons le plein de bois pour l’hiver.
  We are stocking up on wood for the winter.
• Elle a fait le plein de produits de beauté à la parfumerie.
  She stocked up on beauty products at the perfumery.
• Ils font le plein de bonnes idées en lisant des livres.
  They are gathering lots of good ideas by reading books.

Figurative use: maximum amount of something abstract

It can also mean to gather or achieve a large amount of something non-material, like energy, happiness, or votes.

• Après les vacances, j’ai fait le plein d’énergie.
  After the holidays, I am full of energy.
• Le candidat a fait le plein des voix dans les grandes villes.
  The candidate got the most votes in the big cities.
• On fait le plein de bonne humeur avec cette musique.
  This music fills us with good cheer.
• Il va à la montagne pour faire le plein d’air pur.
  He goes to the mountains to get his fill of fresh air.

Synonyms and alternatives

• For filling a tank: mettre de l’essence (to put in gas), prendre de l’essence (to get gas).
• For stocking up: s’approvisionner en (to stock up on), faire des provisions de (to get supplies of), acheter en grande quantité (to buy in large quantity).
• For gathering abstract things: accumuler (to accumulate), engranger (to gather in, to store up), récolter (to reap, to gather).

Summary

• Faire le plein literally means to fill a fuel tank.
• With de, faire le plein de means to stock up on something material.
• It is also used to talk about getting a maximum amount of something abstract like energy or support.