What the “.9” After Gas Prices Really Means

It denotes nine‑tenths of a cent per gallon: a posted price of $3.59 9 means $3.599 per gallon. Stations typically display prices to the tenth of a cent on roadside signs and pumps, then calculate your total purchase at that thousandths‑of‑a‑dollar rate and round the final bill to the nearest cent.

How It Works at the Pump

When you see $3.59 with a small “9/10,” the true per‑gallon price is $3.599. Pumps compute your cost using that three‑decimal figure, reflecting tenths of a cent, and then round your final transaction to the nearest whole cent because U.S. currency settles in cents.

The steps below illustrate how the fractional pricing translates from the sign to your receipt.

1. Posted price: $3.59 9 = $3.599 per gallon.
2. Pump multiplies gallons dispensed by $3.599 (e.g., 10.000 gal × $3.599 = $35.99).
3. The total you pay is rounded to the nearest cent (most pumps already show a two‑decimal running total).
4. Your receipt typically shows the per‑gallon price to three decimals (e.g., $3.599) and the total to two decimals (e.g., $35.99).

In practice, you’re charged exactly what the math dictates at $X.XXX per gallon; only the final amount is rounded to two decimals to match legal tender.

Why Stations Use Nine‑Tenths Pricing

The “9/10” suffix is both historical and strategic. Its persistence comes from a mix of regulation, competition, and consumer psychology.

• Historical roots: Fractional‑cent gas pricing became common during the 1930s as taxes and price wars pushed retailers to fine‑tune posted prices below whole‑cent increments.
• Regulatory compatibility: State weights‑and‑measures rules allow (and pumps support) pricing in tenths of a cent, so retailers can legally post and charge fractional‑cent prices.
• Competitive signaling: Ending in .9 lets stations undercut a rival’s whole‑cent price without a full one‑cent drop.
• Psychological pricing: The left‑digit effect makes $3.59 9 feel more like $3.59 than $3.60, even though the difference is only one‑tenth of a cent.
• Industry convention: Once widespread, .9 became the default ending in the U.S., reinforcing expectations among operators and customers.

While some markets occasionally use other fractional endings, .9 remains the standard in the United States because it combines small pricing flexibility with familiar signage.

Is It Legal? What Regulations Say

Yes. In the U.S., fractional‑cent pricing is lawful, and pumps are certified by state or local weights‑and‑measures officials to dispense and compute at three decimal places. Most jurisdictions require that the posted price include all applicable taxes and that any dual cash/credit pricing be clearly disclosed on signs and at the dispenser. Rules also cover the legibility and size of numerals so the “9/10” isn’t misleading. Specifics vary by state and municipality, but the core principle is transparency: the price you see is the price used to compute your purchase.

Outside the U.S.

Canada also commonly posts fuel prices to the tenth of a cent (e.g., 159.9¢/L), with totals rounded to the nearest cent at payment. Other countries may require whole‑unit pricing (per liter or per gallon) or allow finer increments depending on local regulations and pump standards.

What You’ll See on Your Receipt

Receipts tend to make the fractional pricing explicit, even if the roadside sign uses a small “9/10” symbol. Here’s what to expect.

• Per‑gallon (or per‑liter) unit price displayed to three decimals, e.g., $3.599.
• Total gallons dispensed to three decimals, e.g., 12.347 gal.
• Extended price computed at full precision, with the final total rounded to two decimals, e.g., $44.42.
• If cash and credit prices differ, the applicable unit price for your payment method is shown.

This layout ensures you can verify the arithmetic from unit price to total, including how rounding was applied.

Quick Examples

These examples show how the “9/10” pricing affects real‑world totals at common volumes.

• $3.59 9 per gallon × 10.000 gal = $35.99 (no rounding change needed).
• $3.59 9 per gallon × 14.200 gal = $51.1058 → $51.11 after rounding.
• $4.09 9 per gallon × 8.735 gal = $35.804765 → $35.80 after rounding.

The effect of the nine‑tenths is small per gallon but exact across the full purchase; over large volumes, those tenths of a cent add up precisely before the final cent‑level rounding.

Bottom Line

The “.9” after gas prices represents nine‑tenths of a cent, making $3.59 9 equal to $3.599 per gallon. Pumps charge you at that three‑decimal rate and round your total to the nearest cent, a practice that’s legal, regulated, and rooted in both history and pricing strategy.

How to read gas prices in the US?

For example, if the sign displays $3.59, it means that one gallon of gasoline costs $3.59. But why do these prices keep fluctuating? Gasoline prices are influenced by various factors such as crude oil prices, taxes, transportation costs, and even supply and demand dynamics in the market.

What does the 9 mean on gas?

The practice of tacking 9/10 of a cent on the end of a gas price goes back to when gas cost only pennies per gallon and was a tax imposed by state and federal governments. Gas stations added the fraction of a cent on the end of the price instead of rounding up the price.

When did gas hit $1.00 a gallon?

While gas stayed below a dollar from 1929 until 1980 (a period of 51 years) it doubled in the four years from 1979 to 1983. I guess we showed them. To be fair it did go back down slightly in the late 1980’s, but after that, a dollar a gallon gas was just a fond memory.

What is the fraction after the gas price?

(NEXSTAR) – In case gas prices weren’t high enough already, there’s always that pesky fraction added onto the end: nine-tenths of a cent tacked on to every gallon. You’ll usually see this odd pricing posted at the gas station (and pretty much nowhere else).