Is the iridium plug
actually worth the upgrade?
Iridium plugs cost 4× as much per unit as copper. They also last 3.3× longer (100K vs 30K miles) and give a small fuel-efficiency uplift (~1.2%) over a horizon. The calculator works out whether the longer life and small gas savings actually beat the upfront cost over your driving horizon — including the labour cost of fewer swaps.
plug upgrade comparison
Current plug type
Target plug type
Engine plug count
Miles per year
Vehicle MPG
Gas price ($/gal)
Labour per swap ($)
Horizon (years)
over 8 years
UPGRADE SAVES
+$314
vs continuing on Copper over 8 years
where the upgrade pays off
Plug ratings (miles to replacement): Copper 30K · Platinum 60K · Iridium 100K. Fuel-efficiency gains are modest and well-documented: +0.5% upgrading copper→platinum (cleaner combustion), +1.2% upgrading copper→iridium (smaller electrode = lower voltage = more complete burn). Iridium gains are largest in older engines with worn plugs at higher mileage. Treat numbers as upper bound; real gains depend on engine state.