Gas Mileage Trip Cost

What "MPG" actually means for your wallet

A 5 MPG difference matters more at the low end than the high end. Going from 20 to 25 MPG saves more fuel than going from 35 to 40 MPG over the same miles. Use gallons per 100 miles as a better mental model:

• 15 MPG: 6.7 gallons per 100 miles
• 20 MPG: 5.0 gallons per 100 miles
• 25 MPG: 4.0 gallons per 100 miles
• 30 MPG: 3.3 gallons per 100 miles
• 40 MPG: 2.5 gallons per 100 miles
• 50 MPG (hybrid): 2.0 gallons per 100 miles

That's why fleet operators care more about the jump from a 15 MPG truck to a 20 MPG truck than from a 30 MPG sedan to a 35 MPG sedan.

The biggest factors that destroy MPG

• Aggressive driving: Jackrabbit starts and hard braking can cut MPG by 15-30%.
• High speeds: Every 5 mph over 50 costs ~7% MPG. Going 80 mph vs 65 mph cuts MPG ~20%.
• Cold starts and short trips: A cold engine runs rich for 3-5 minutes. Short trips averaged 10-15% worse than highway driving.
• Tire pressure: Every 1 PSI under spec costs ~0.3% MPG. A whole set 5 PSI low = 6% drop.
• Roof rack/cargo box: Drag costs 5-25% at highway speeds — remove between trips.
• Idling: Modern engines: idle longer than 10 seconds, restart uses less fuel. Newer cars with auto stop-start do this automatically.

Hypermiling techniques

• Coast in gear, not neutral. Modern fuel-injected engines cut fuel completely when off-throttle in gear.
• Pulse and glide: Accelerate efficiently to 5 mph above your target, coast back down. Smooth — not aggressive.
• Read traffic: Anticipating stops 2-3 cars ahead lets you coast to the light instead of braking hard.
• Use cruise control on flat highway. On hilly terrain, manual throttle saves more.
• Drive at off-peak times. Stop-and-go traffic can halve MPG vs free-flow.

EV math: per-mile comparison

To compare an EV's electricity cost to gas, convert kWh per 100 miles to gallons per 100 miles:

• Tesla Model 3 (~26 kWh/100 mi at $0.15/kWh): $3.90 per 100 miles
• Toyota Prius (52 MPG at $3.50/gallon): $6.73 per 100 miles
• Honda Civic (35 MPG at $3.50/gallon): $10.00 per 100 miles
• F-150 (20 MPG at $3.50/gallon): $17.50 per 100 miles

EV-vs-gas savings depend heavily on your local electricity rate. California ($0.30+/kWh) closes the gap; Texas/Tennessee ($0.10-0.13/kWh) makes EVs dirt-cheap to operate.

Maintenance that affects MPG

• Air filter: Dirty filter can cost 5-10% MPG. Change every 30-45k miles.
• Spark plugs: Worn plugs cause misfires and rich-running. Standard plugs: 30k. Iridium: 100k.
• Oxygen sensor: Slow-responding O2 sensor can cut MPG 15-20%. Often the culprit when MPG drops suddenly.
• Engine oil: Use the viscosity grade in your manual. Heavier oil "for protection" costs MPG. Synthetic generally 1-2% better than conventional.
• Tires: Low-rolling-resistance tires can recover 2-4% MPG vs aggressive all-terrains.