Same Finger N-gram

A same-finger n-gram (SFN) is a n-gram that is typed entirely with one finger.

Note

This terminology “SFN” is unique to AKLDB, but it is a generalization of existing concepts.

Take a look at the left middle finger’s column in QWERTY:

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On this column:

• ed (as in “tied”) is a same-finger bigram,
• dec (as in “decor”) is a same-finger trigram,
• c_d (as in “cod”) is a 1st order same-finger skipgram, and
• c__e (as in “care”) is a 2nd order same-finger skipgram.

Same Finger Bigram

A same-finger bigram (SFB) is a bigram typed with one finger. In some older sources, this metric is called same-finger utilization (SFU).

$\text{SFB}\% = \dfrac {\text{\# of same-finger bigrams}} {\text{\# of bigrams}}$

Because pressing multiple times with the same finger is slower than pressing different keys with different fingers, many contemporary layouts, especially from the AKL Discord, heavily optimize for a low SFB ratio. However, some comfort-focused layouts that aren’t optimized for speed allow for a higher SFB ratio in exchange for other, often idiosyncratic, stats.

Note

Layout analyzers generally exclude pressing the same key twice (e.g. the ee bigram in feed) from their SFB stats, since such SFBs were not possible to eliminate before the advent of magic keys. AKLDB maintains this convention.

Lowest SFB% Layouts

Note

Same-key bigrams are included in these stats. This will be changed in a future update.

Rank	Layout	SFB%
1	Whirl (2024)	0.46%
2	Magic Sturdy (2023)	0.52%
3	Nordrassil Abyssal (2024)	1.21%
4	Nordrassil Vanilla (2024)	1.25%
5	Cistern (2025)	1.79%
6	Night (2024)	2.32%
7	Whorf (2021)	2.35%
8	Dusk (2024)	2.37%
9	Dhorf (2023)	2.39%
10	Pine v2 (2021)	2.46%

Same Finger Trigram

A same-finger trigram (SFT) a trigram typed with one finger.

$\text{SFT}\% = \dfrac {\text{\# of same-finger trigrams}} {\text{\# of trigrams}}$

SFTs are common on legacy layouts such as QWERTY. Contemporary optimized layouts have a very low SFT ratio, so they are typically not an issue.

Lowest SFT% Layouts

Rank	Layout	SFT%
1	Whirl (2024)	0.01%
2	Nordrassil Vanilla (2024)	0.01%
3	Nordrassil Abyssal (2024)	0.08%
4	Magic Sturdy (2023)	0.13%
5	Hands Down™ Neu Hardened Metals Vibranium b (2022)	0.16%
6	Hands Down™ Neu Hardened Metals Vibranium v (2022)	0.16%
7	Hands Down™ Neu Élan (2022)	0.17%
8	Hands Down™ Neu Hardened Metals Vibranium p (2022)	0.17%
9	ISRT Standard (2021)	0.17%
10	ISRT Angle Mod (2021)	0.17%

Same Finger Skipgram

A same-finger skipgram (SFS) is a skipgram typed with one finger.

The order of the SFS is the same as the order of the skipgram. Thus:

$\text{SFS}_1\% = \dfrac {\text{\# of 1st order same-finger skipgrams}} {\text{\# of trigrams}}$

SFS1 is also called disjoint same-finger bigram (dSFB) in some older literature, especially among AKL Discord members.

Lowest SFS1% Layouts

Rank	Layout	SFS1%
1	Cistern (2025)	5.57%
2	Dusk (2024)	6.33%
3	Night (2024)	6.56%
4	Recurva (2023)	6.57%
5	Semimak Original (2021)	6.69%
6	Hands Down™ Alt tx (2021)	6.70%
7	Semimak JQ (2021)	6.71%
8	Whirl (2024)	6.73%
9	Hands Down™ Alt nx (2021)	6.79%
10	Hands Down™ Neu Precious Metals Gold (2022)	6.87%

Higher order SFSs

Higher order SFSs are also possible:

$\text{SFS}_n\% = \dfrac {\text{\# of } n\text{-th order same-finger skipgrams}} {\text{\# of } (n+2)\text{-grams}}$

Semi pioneered the use of SFS in keyboard layout analysis. In Semi’s analysis:

$\text{SFS}\% = \sum_{i=0}^\infty \text{SFS}_i\%\cdot2^\frac1i$

For computational complexity purposes, AKLDB only analyses SFS1%.

Distance

Going back to the QWERTY example,

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We call ed a 1u SFB, since the finger travels a distance of 1 unit to move from the e key to the d key.

Note

On row-staggered keyboards, the distance between e and d is actually $\sqrt{1^2 + \frac14^2}$, or about 1.03u, because of the horizontal offset. For the purposes of layout metrics, we round the distance to the nearest 0.5u.

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The bigram ec takes longer to type than ed because the e and c keys are farther away from each other than the e and d keys. On ortholinear keyboards, the distance is exactly 2u. On row-staggered keyboards, the distance is $\sqrt{2^2+\frac34^2}$, or about 2.14u; we count this as a 2u SFB after rounding to the nearest 0.5u.

Sources

“SFBs, SFSs and distance,” Keyboard Layouts Doc (3rd edition)