ET Correction Calculator

Enter your elapsed time, trap speed and the conditions you ran in. This applies NHRA's published correction factors to show what the same pass would have been worth on a sea-level standard day — the only fair way to compare runs made on different days.

Why the same car runs different numbers

An engine makes power by burning oxygen, and the amount of oxygen in a lungful of air depends on how dense that air is. Heat expands it, altitude thins it, and humidity displaces some of the oxygen with water vapour. The car did not get slower — the air got worse.

Density altitude rolls all three effects into one number, and correction factors turn that number into a multiplier on your ET and trap speed. This is the same idea behind bracket racing dial-ins and why a track's records almost always fall on a cold night.

What correction can and cannot tell you

Correction is an estimate built from published averages, not a measurement. It does not know your gearing, your tyres, how well you launched, or whether you lifted. Two cars with the same corrected ET did not necessarily make the same power. Use it to compare your own runs fairly across days — that is what it is genuinely good at.

It also assumes a naturally aspirated engine. If you are boosted, the real loss is smaller than the table suggests, so read the corrected number as the most it could be worth rather than a firm figure.

Common questions

What is a corrected ET?

Your elapsed time adjusted for the air you ran in. Hot, humid or high-altitude air makes less power, so a run there is worth more than the raw number suggests. Correcting to a standard day lets you compare a July pass against a November one honestly.

Are these the official NHRA correction factors?

Yes — the anchors used here are NHRA's own published ET and MPH correction values, interpolated between the published points. They are defined for naturally aspirated engines.

Why does my turbo car not lose as much at altitude?

Because a turbocharger or supercharger compresses the intake air to hit a target manifold pressure, so it recovers a large share of what thin air takes away. Published correction factors assume a naturally aspirated engine, so applying them to a boosted car overstates the loss. Treat the corrected number as an upper bound.

Should correcting make my ET faster or slower?

If you ran in thin air (high DA), correcting makes the number quicker, because the same car would have gone faster in good air. If you ran in unusually cold, dense, low-altitude air, correcting moves the other way — that air was already better than standard.