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Lambda to AFR Chart & Air Fuel Ratio Calculator

Posted by CMB on Nov 25th 2025

Lambda to AFR Chart & Air Fuel Ratio Calculator

Lambda to AFR: Quick Answers

Lambda is the ratio of actual air-fuel ratio to stoichiometric. AFR = Lambda × stoichiometric AFR. For pump gasoline stoich is 14.7, so Lambda 0.85 = 12.50 AFR. Here are the values people look up most:

LambdaGas AFRE85 AFRDiesel AFR
0.7511.027.3510.88
0.7811.477.6411.31
0.8011.767.8411.60
0.8212.058.0411.89
0.8312.208.1312.04
0.8412.358.2312.18
0.8512.498.3312.32
0.8812.948.6212.76
0.9013.238.8213.05
0.9513.969.3113.77
1.0014.709.8014.50

Going the other way, divide by stoich: 12.5 AFR = 0.850 Lambda and 11.5 AFR = 0.782 Lambda on gasoline. Use the calculator below for any value, on any fuel.

AFR / Lambda Converter Calculator

Enter a value in either field to instantly convert between AFR and Lambda. Works for gasoline (stoich 14.7), E85 (stoich 9.8), and diesel (stoich 14.5).

Enter a value above to see the conversion
Quick Reference (Gasoline):
Rich: AFR 11.5 = Lambda 0.78 | Target WOT: AFR 12.5 = Lambda 0.85 | Stoich: AFR 14.7 = Lambda 1.00 | Lean cruise: AFR 15.5 = Lambda 1.05

Full Lambda to AFR Conversion Chart

Every lambda value from 0.50 to 1.20, converted for gasoline, E85, E100, methanol and diesel.

Lambda Gas AFR  E85 AFR E100 AFR Methanol AFR Diesel AFR
0.50 7.35 4.88 4.49 3.23 7.25
0.51 7.50 4.98 4.58 3.29 7.40
0.52 7.64 5.08 4.67 3.36 7.54
0.53 7.79 5.17 4.76 3.42 7.69
0.54 7.94 5.27 4.85 3.49 7.83
0.55 8.09 5.37 4.94 3.55 7.98
0.56 8.23 5.47 5.03 3.62 8.12
0.57 8.38 5.56 5.12 3.68 8.27
0.58 8.53 5.66 5.21 3.74 8.41
0.59 8.67 5.76 5.30 3.81 8.56
0.60 8.82 5.86 5.39 3.87 8.70
0.61 8.97 5.95 5.48 3.94 8.85
0.62 9.11 6.05 5.57 4.00 8.99
0.63 9.26 6.15 5.66 4.07 9.14
0.64 9.41 6.25 5.75 4.13 9.28
0.65 9.56 6.34 5.84 4.20 9.43
0.66 9.70 6.44 5.93 4.26 9.57
0.67 9.85 6.54 6.02 4.33 9.72
0.68 10.00 6.64 6.11 4.39 9.86
0.69 10.14 6.73 6.20 4.46 10.01
0.70 10.29 6.83 6.29 4.52 10.15
0.71 10.44 6.93 6.38 4.58 10.30
0.72 10.58 7.03 6.47 4.65 10.44
0.73 10.73 7.12 6.56 4.71 10.59
0.74 10.88 7.22 6.65 4.78 10.73
0.75 11.03 7.32 6.74 4.84 10.88
0.76 11.17 7.42 6.83 4.91 11.02
0.77 11.32 7.52 6.92 4.97 11.17
0.78 11.47 7.61 7.01 5.04 11.31
0.79 11.61 7.71 7.10 5.10 11.46
0.80 11.76 7.81 7.19 5.17 11.60
0.81 11.91 7.91 7.27 5.23 11.75
0.82 12.05 8.00 7.36 5.29 11.89
0.83 12.20 8.10 7.45 5.36 12.04
0.84 12.35 8.20 7.54 5.42 12.18
0.85 12.50 8.30 7.63 5.49 12.33
0.86 12.64 8.39 7.72 5.55 12.47
0.87 12.79 8.49 7.81 5.62 12.62
0.88 12.94 8.59 7.90 5.68 12.76
0.89 13.08 8.69 7.99 5.75 12.91
0.90 13.23 8.78 8.08 5.81 13.05
0.91 13.38 8.88 8.17 5.88 13.20
0.92 13.52 8.98 8.26 5.94 13.34
0.93 13.67 9.08 8.35 6.00 13.49
0.94 13.82 9.17 8.44 6.07 13.63
0.95 13.97 9.27 8.53 6.13 13.78
0.96 14.11 9.37 8.62 6.20 13.92
0.97 14.26 9.47 8.71 6.26 14.07
0.98 14.41 9.56 8.80 6.33 14.21
0.99 14.55 9.66 8.89 6.39 14.36
1.00 14.70 9.76 8.98 6.46 14.50
1.01 14.85 9.86 9.07 6.52 14.65
1.02 14.99 9.96 9.16 6.59 14.79
1.03 15.14 10.05 9.25 6.65 14.94
1.04 15.29 10.15 9.34 6.71 15.08
1.05 15.44 10.25 9.43 6.78 15.23
1.06 15.58 10.35 9.52 6.84 15.37
1.07 15.73 10.44 9.61 6.91 15.52
1.08 15.88 10.54 9.70 6.97 15.66
1.09 16.02 10.64 9.79 7.04 15.81
1.10 16.17 10.74 9.88 7.10 15.95
1.11 16.32 10.83 9.97 7.17 16.10
1.12 16.46 10.93 10.06 7.23 16.24
1.13 16.61 11.03 10.15 7.30 16.39
1.14 16.76 11.13 10.24 7.36 16.53
1.15 16.91 11.22 10.33 7.43 16.68
1.16 17.05 11.32 10.42 7.49 16.82
1.17 17.20 11.42 10.51 7.55 16.97
1.18 17.35 11.52 10.60 7.62 17.11
1.19 17.49 11.61 10.69 7.68 17.26
1.20 17.64 11.71 10.78 7.75 17.40

Target AFR and Lambda by Application

Lambda is the more useful number because the target does not change when the fuel does. A naturally aspirated engine wants roughly the same lambda on gas or E85 — the AFR number looks completely different, but the mixture is the same.

ConditionLambdaGas AFR
Idle / light cruise1.0014.7
Lean cruise (economy)1.02 - 1.0515.0 - 15.4
Naturally aspirated WOT0.85 - 0.8812.5 - 12.9
Boosted WOT (low boost)0.80 - 0.8311.8 - 12.2
Boosted WOT (high boost)0.75 - 0.7811.0 - 11.5

These are starting points, not a tune. Actual targets depend on compression, boost, camshaft, fuel quality and knock behavior. Always confirm with a wideband and datalogs.

Frequently Asked Questions

What is 0.85 lambda in AFR?
On gasoline, 0.85 lambda equals 12.50 AFR. On E85 it equals 8.33 AFR, and on diesel 12.33 AFR.

What is 0.78 lambda in AFR?
On gasoline, 0.78 lambda equals 11.47 AFR — a common high-boost wide-open-throttle target.

What lambda is 12.5 AFR?
12.5 AFR on gasoline is 0.850 lambda, a typical naturally aspirated WOT target.

Is lambda better than AFR?
For tuning, yes. Lambda is fuel-independent, so 0.85 means the same mixture whether you run pump gas, E85 or methanol. AFR only makes sense once you know which fuel the number refers to.

What is stoichiometric AFR for E85?
Roughly 9.8:1, versus 14.7:1 for gasoline. E85 needs about 30 percent more fuel by mass for the same mixture, which is why injectors and fuel pumps often need upgrading.

Need Help Dialing In Your Tune?

Reading lambda correctly is the easy part — getting the calibration right is the work. N2 Speed builds custom calibrations for Dodge, RAM, Jeep, Chrysler, GM and Ford platforms.

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