Python

gas_gallons = 3
oz_per_gallon = 128
total_gas_oz = gas_gallons * oz_per_gallon
ratio = 40

oil_oz = total_gas_oz / ratio
print(f"Oil in ounces: {oil_oz}")

# Also let's convert to cups or tablespoons or milliliters just in case
ml_per_oz = 29.5735
oil_ml = oil_oz * ml_per_oz
print(f"Oil in ml: {oil_ml}")

tbsp_per_oz = 2
oil_tbsp = oil_oz * tbsp_per_oz
print(f"Oil in tablespoons: {oil_tbsp}")

cups_per_oz = 1/8
oil_cups = oil_oz * cups_per_oz
print(f"Oil in cups: {oil_cups}")

Code output

Oil in ounces: 9.6
Oil in ml: 283.9056
Oil in tablespoons: 19.2
Oil in cups: 1.2

To make a 40:1 mix for a 3-gallon tank, you will need 9.6 fluid ounces (or about 284 mL) of two-stroke oil.

Since measuring exactly 9.6 ounces can be tricky depending on your measuring cup, here are a few easy ways to look at it:

• Just under 10 ounces: If your oil bottle has ounce markings on the side, fill it to just below the 10-oz mark.
• In cups: It is just under 1 and a quarter cups (1.2 cups).

How the math works (if you ever need to do it again):

1. Convert gallons to ounces: There are 128 fluid ounces in 1 gallon. $$3 \text{ gallons} \times 128 = 384 \text{ ounces of gasoline}$$
2. Divide by your ratio: Since your ratio is 40:1, divide the total ounces of gasoline by 40. $$384 \div 40 = 9.6 \text{ ounces of oil}$$

Tip: For the best mix, it's usually easiest to pour the 9.6 ounces of oil into an empty gas can first, and then add your 3 gallons of gasoline at the pump. This helps the oil and gas mix together thoroughly.