What “9/10” Means on Gas Prices — The Odd Fraction, Explained

It means nine-tenths of a cent. When a station posts a price like $3.59 9/10, the actual price is $3.599 per gallon. This fractional cent is a long-standing industry convention rooted in early tax rules and now used largely as psychological pricing; your total at the pump is calculated to the thousandth of a dollar and then rounded to the nearest cent on your receipt. Many Reddit threads ask this, but the meaning is straightforward and current across most U.S. gas stations.

What you’re really paying at the pump

The “9/10” is 0.9 of a cent added to the posted dollar-and-cent price. So, $3.59 9/10 equals $3.599 per gallon. Pumps compute your total using that precise price and the exact gallons dispensed, then your final charge is rounded to the nearest cent (as U.S. currency doesn’t use tenths of a cent).

Example: If you buy 12.3 gallons at $3.59 9/10, the math is 12.3 × $3.599 = $44.2677, which appears on your receipt as $44.27 after rounding.

Why the 9/10 exists

Fractional-cent gas pricing dates to the 1920s–1930s, when gas was cheap and taxes and competition nudged prices in tenths of a cent. Mechanical pump meters supported tenth-cent precision, and the 9/10 ending evolved into a marketing norm that makes a price look a full cent lower (e.g., $3.59 9/10 instead of $3.60). The convention persists across the U.S. and in some other countries even though the original tax rationale is largely historical.

Legality and how it appears on receipts

Fractional-cent pricing is legal in the U.S. Regulators calibrate pumps to ensure accurate measurement at that precision. While the per-gallon price includes the 9/10, your total is settled in whole cents after exact calculation and rounding. That’s why you’ll often see an amount like $44.27 rather than $44.26 or $44.28—the pennies reflect the rounded total of a fractional-cent-per-gallon price multiplied by your gallons.

Quick examples

The following examples illustrate how “9/10” translates into real prices and totals you might see.

1. $3.49 9/10 per gallon = $3.499. For 10 gallons, total = $34.99.
2. $4.19 9/10 per gallon = $4.199. For 12 gallons, total = $50.388 → receipt rounds to $50.39.
3. Difference vs. the “next” even cent: $3.599 vs. $3.600 is $0.001 per gallon. On 15 gallons, that’s 1.5 cents.

As these examples show, the fractional-cent difference is tiny per fill-up, but it’s ubiquitous and adds up in aggregate across millions of gallons sold.

Key takeaways

Keep these points in mind the next time you see “9/10” on a station sign.

• “9/10” = 0.9 of a cent, so $X.YZ 9/10 equals $X.YZ9 per gallon.
• Your pump calculates with full precision; your receipt rounds to the nearest cent.
• The practice began decades ago and now functions mainly as psychological pricing.

Together, these points explain why the notation persists and how it affects what you pay—precisely, but minimally, on each transaction.

Summary

On gas price signs, “9/10” means nine-tenths of a cent added to the posted dollars and cents, making $3.59 9/10 equal $3.599 per gallon. It’s a legacy of early pricing and tax practices that survives today as a marketing convention; pumps compute your total using that exact price, and your final bill rounds to the nearest cent.

What does 9/10 of a gallon mean?

“9/10 of a gallon” refers to the fractional pricing, or psychological pricing, used in gasoline sales, where a price is listed at a fraction of a cent (like $3.999 per gallon) instead of a round number ($4.00) to make the price seem lower to consumers. This practice originated in the 1930s to absorb small government fuel taxes without shocking consumers with a full-cent increase, but it continues today as a marketing strategy even though the fraction itself has no real cash value and is rounded for payment.
 
Why gas prices end in 9/10 of a cent: 

• Psychological Pricing: Opens in new tabUsing prices like $3.999 instead of $4.00 makes the price seem substantially lower to consumers, a common marketing tactic known as “just-below pricing”. 
• Historical Tax Incorporation: Opens in new tabThe practice started when federal and state gasoline taxes were introduced as fractions of a cent, which were then passed on to consumers by gas stations. 
• Avoiding a Full Cent Increase: Opens in new tabIn the 1930s, adding a full penny to a 10-cent gallon of gas would have been a significant 10% increase, so stations added a fraction of a cent instead to soften the impact. 
• Competitive Pricing: Opens in new tabIf one gas station started pricing at a full cent, it might appear more expensive than competitors who use the 9/10ths-of-a-cent pricing. 

How it works in practice:

• Not a Real Coin: Opens in new tabSince there is no 1/10th-of-a-cent coin, you do not pay the exact amount listed. 
• Rounding: Opens in new tabThe final price you pay, whether with cash or credit, is rounded to the nearest cent. 
• Meaningless Fraction: Opens in new tabThe fraction of a cent is technically meaningless in today’s economy, but it continues because it is a deeply ingrained marketing practice that gas stations and consumers are used to. 

What does the number mean on gas?

The “gas numbers” you see on a pump are octane ratings, which measure a gasoline’s resistance to pre-ignition (or “knock”) under compression in an engine. Higher octane numbers (like 91 or 93) indicate greater fuel stability and are suitable for high-compression engines found in performance or turbocharged cars, while lower numbers (like 87) are standard for most vehicles and are less likely to cause damage from premature ignition.
 
What Octane Ratings Mean

• Knock Resistance: Octane rating indicates how much pressure fuel can withstand before it spontaneously ignites. 
• Fuel Stability: A higher octane number means the fuel is more stable and less likely to detonate prematurely in the engine. 
• Engine Damage: Premature ignition, or “engine knock,” can cause severe damage, so using the appropriate octane for your engine is crucial. 

Common Octane Grades

• Regular (87 Octane): The standard, lowest octane fuel, suitable for most vehicles. 
• Mid-grade (89-90 Octane): A slightly higher octane fuel, sometimes called “Super”. 
• Premium (91-94 Octane): The highest grade of gasoline, recommended for high-compression, turbocharged, or supercharged engines. 

Why Higher Octane Is Not Always Better

• Performance Cars: Opens in new tabHigh-compression engines in performance vehicles require the higher stability of premium fuel to prevent knock. 
• Most Vehicles: Opens in new tabFor standard engines, using premium gas is not necessary and does not offer increased performance or better fuel economy. 
• Energy Content: Opens in new tabAll grades of gasoline have the same energy content; the difference is in their resistance to detonation. 

Why do they sell gas at 9-10 of a gallon?

Over time, fuel retailers evolved to pricing at 0.9 cents. The reason is marketing. Retail experts have long known that goods prices slightly less than those priced at a whole number sound far less expensive. Something that is priced at $9.99 seems a lot less expensive than something priced at $10.

What does the 9 over 10 mean in gas prices?

Additionally, Miles says that ending something with a fraction of a cent, like 9/10, gives the illusion that pricing is not as high as it seems. “It’s like the old trick of pricing something ‘3 for $1’ rather than 34 cents each,” he notes.