Flash Guide Number Distance Calculator Reference Values

Calculate flash working distance from guide number, aperture, and ISO for manual flash photography.

Author

Dr. Mateo Silva Herrera

Photography editorial contributor

Colombian urban planner with a PhD from UCL, designing resilient infrastructure for flood-prone cities

Reviewed for accuracy by

Prof. Ingrid Johansson

Photography content reviewer

Norwegian political scientist at the University of Oslo, studying democratic resilience in Nordic welfare states

Last updatedFebruary 22, 2026

PublishedFebruary 22, 2026

Reference Value Index

This page lists 144 reference values for quick browsing and lookup.

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All Reference Values

Reference Table

Flash Guide Number Distance Calculator reference values
Flash Scenario	Distance (m)	Distance (ft)
GN 12 m, f/1.4, ISO 100	8.57 m flash distance	28.12
GN 12 m, f/1.4, ISO 200	12.12 m flash distance	39.77
GN 12 m, f/1.4, ISO 400	17.14 m flash distance	56.24
GN 12 m, f/2, ISO 100	6 m flash distance	19.69
GN 12 m, f/2, ISO 200	8.49 m flash distance	27.84
GN 12 m, f/2, ISO 400	12 m flash distance	39.37
GN 12 m, f/2.8, ISO 100	4.29 m flash distance	14.06
GN 12 m, f/2.8, ISO 200	6.06 m flash distance	19.88
GN 12 m, f/2.8, ISO 400	8.57 m flash distance	28.12
GN 12 m, f/4, ISO 100	3 m flash distance	9.84
GN 12 m, f/4, ISO 200	4.24 m flash distance	13.92
GN 12 m, f/4, ISO 400	6 m flash distance	19.69
GN 12 m, f/5.6, ISO 100	2.14 m flash distance	7.03
GN 12 m, f/5.6, ISO 200	3.03 m flash distance	9.94
GN 12 m, f/5.6, ISO 400	4.29 m flash distance	14.06
GN 12 m, f/8, ISO 100	1.5 m flash distance	4.92
GN 12 m, f/8, ISO 200	2.12 m flash distance	6.96
GN 12 m, f/8, ISO 400	3 m flash distance	9.84
GN 12 m, f/11, ISO 100	1.09 m flash distance	3.58
GN 12 m, f/11, ISO 200	1.54 m flash distance	5.06
GN 12 m, f/11, ISO 400	2.18 m flash distance	7.16
GN 12 m, f/16, ISO 100	0.75 m flash distance	2.46
GN 12 m, f/16, ISO 200	1.06 m flash distance	3.48
GN 12 m, f/16, ISO 400	1.5 m flash distance	4.92
GN 20 m, f/1.4, ISO 100	14.29 m flash distance	46.87
GN 20 m, f/1.4, ISO 200	20.2 m flash distance	66.28
GN 20 m, f/1.4, ISO 400	28.57 m flash distance	93.74
GN 20 m, f/2, ISO 100	10 m flash distance	32.81
GN 20 m, f/2, ISO 200	14.14 m flash distance	46.4
GN 20 m, f/2, ISO 400	20 m flash distance	65.62
GN 20 m, f/2.8, ISO 100	7.14 m flash distance	23.43
GN 20 m, f/2.8, ISO 200	10.1 m flash distance	33.14
GN 20 m, f/2.8, ISO 400	14.29 m flash distance	46.87
GN 20 m, f/4, ISO 100	5 m flash distance	16.4
GN 20 m, f/4, ISO 200	7.07 m flash distance	23.2
GN 20 m, f/4, ISO 400	10 m flash distance	32.81
GN 20 m, f/5.6, ISO 100	3.57 m flash distance	11.72
GN 20 m, f/5.6, ISO 200	5.05 m flash distance	16.57
GN 20 m, f/5.6, ISO 400	7.14 m flash distance	23.43
GN 20 m, f/8, ISO 100	2.5 m flash distance	8.2
GN 20 m, f/8, ISO 200	3.54 m flash distance	11.6
GN 20 m, f/8, ISO 400	5 m flash distance	16.4
GN 20 m, f/11, ISO 100	1.82 m flash distance	5.97
GN 20 m, f/11, ISO 200	2.57 m flash distance	8.44
GN 20 m, f/11, ISO 400	3.64 m flash distance	11.93
GN 20 m, f/16, ISO 100	1.25 m flash distance	4.1
GN 20 m, f/16, ISO 200	1.77 m flash distance	5.8
GN 20 m, f/16, ISO 400	2.5 m flash distance	8.2
GN 28 m, f/1.4, ISO 100	20 m flash distance	65.62
GN 28 m, f/1.4, ISO 200	28.28 m flash distance	92.8
GN 28 m, f/1.4, ISO 400	40 m flash distance	131.23
GN 28 m, f/2, ISO 100	14 m flash distance	45.93
GN 28 m, f/2, ISO 200	19.8 m flash distance	64.96
GN 28 m, f/2, ISO 400	28 m flash distance	91.86
GN 28 m, f/2.8, ISO 100	10 m flash distance	32.81
GN 28 m, f/2.8, ISO 200	14.14 m flash distance	46.4
GN 28 m, f/2.8, ISO 400	20 m flash distance	65.62
GN 28 m, f/4, ISO 100	7 m flash distance	22.97
GN 28 m, f/4, ISO 200	9.9 m flash distance	32.48
GN 28 m, f/4, ISO 400	14 m flash distance	45.93
GN 28 m, f/5.6, ISO 100	5 m flash distance	16.4
GN 28 m, f/5.6, ISO 200	7.07 m flash distance	23.2
GN 28 m, f/5.6, ISO 400	10 m flash distance	32.81
GN 28 m, f/8, ISO 100	3.5 m flash distance	11.48
GN 28 m, f/8, ISO 200	4.95 m flash distance	16.24
GN 28 m, f/8, ISO 400	7 m flash distance	22.97
GN 28 m, f/11, ISO 100	2.55 m flash distance	8.35
GN 28 m, f/11, ISO 200	3.6 m flash distance	11.81
GN 28 m, f/11, ISO 400	5.09 m flash distance	16.7
GN 28 m, f/16, ISO 100	1.75 m flash distance	5.74
GN 28 m, f/16, ISO 200	2.47 m flash distance	8.12
GN 28 m, f/16, ISO 400	3.5 m flash distance	11.48
GN 36 m, f/1.4, ISO 100	25.71 m flash distance	84.36
GN 36 m, f/1.4, ISO 200	36.37 m flash distance	119.31
GN 36 m, f/1.4, ISO 400	51.43 m flash distance	168.73
GN 36 m, f/2, ISO 100	18 m flash distance	59.06
GN 36 m, f/2, ISO 200	25.46 m flash distance	83.52
GN 36 m, f/2, ISO 400	36 m flash distance	118.11
GN 36 m, f/2.8, ISO 100	12.86 m flash distance	42.18
GN 36 m, f/2.8, ISO 200	18.18 m flash distance	59.65
GN 36 m, f/2.8, ISO 400	25.71 m flash distance	84.36
GN 36 m, f/4, ISO 100	9 m flash distance	29.53
GN 36 m, f/4, ISO 200	12.73 m flash distance	41.76
GN 36 m, f/4, ISO 400	18 m flash distance	59.06
GN 36 m, f/5.6, ISO 100	6.43 m flash distance	21.09
GN 36 m, f/5.6, ISO 200	9.09 m flash distance	29.83
GN 36 m, f/5.6, ISO 400	12.86 m flash distance	42.18
GN 36 m, f/8, ISO 100	4.5 m flash distance	14.76
GN 36 m, f/8, ISO 200	6.36 m flash distance	20.88
GN 36 m, f/8, ISO 400	9 m flash distance	29.53
GN 36 m, f/11, ISO 100	3.27 m flash distance	10.74
GN 36 m, f/11, ISO 200	4.63 m flash distance	15.18
GN 36 m, f/11, ISO 400	6.55 m flash distance	21.47
GN 36 m, f/16, ISO 100	2.25 m flash distance	7.38
GN 36 m, f/16, ISO 200	3.18 m flash distance	10.44
GN 36 m, f/16, ISO 400	4.5 m flash distance	14.76
GN 43 m, f/1.4, ISO 100	30.71 m flash distance	100.77
GN 43 m, f/1.4, ISO 200	43.44 m flash distance	142.51
GN 43 m, f/1.4, ISO 400	61.43 m flash distance	201.54
GN 43 m, f/2, ISO 100	21.5 m flash distance	70.54
GN 43 m, f/2, ISO 200	30.41 m flash distance	99.76
GN 43 m, f/2, ISO 400	43 m flash distance	141.08
GN 43 m, f/2.8, ISO 100	15.36 m flash distance	50.38
GN 43 m, f/2.8, ISO 200	21.72 m flash distance	71.25
GN 43 m, f/2.8, ISO 400	30.71 m flash distance	100.77
GN 43 m, f/4, ISO 100	10.75 m flash distance	35.27
GN 43 m, f/4, ISO 200	15.2 m flash distance	49.88
GN 43 m, f/4, ISO 400	21.5 m flash distance	70.54
GN 43 m, f/5.6, ISO 100	7.68 m flash distance	25.19
GN 43 m, f/5.6, ISO 200	10.86 m flash distance	35.63
GN 43 m, f/5.6, ISO 400	15.36 m flash distance	50.38
GN 43 m, f/8, ISO 100	5.38 m flash distance	17.63
GN 43 m, f/8, ISO 200	7.6 m flash distance	24.94
GN 43 m, f/8, ISO 400	10.75 m flash distance	35.27
GN 43 m, f/11, ISO 100	3.91 m flash distance	12.83
GN 43 m, f/11, ISO 200	5.53 m flash distance	18.14
GN 43 m, f/11, ISO 400	7.82 m flash distance	25.65
GN 43 m, f/16, ISO 100	2.69 m flash distance	8.82
GN 43 m, f/16, ISO 200	3.8 m flash distance	12.47
GN 43 m, f/16, ISO 400	5.38 m flash distance	17.63
GN 58 m, f/1.4, ISO 100	41.43 m flash distance	135.92
GN 58 m, f/1.4, ISO 200	58.59 m flash distance	192.22
GN 58 m, f/1.4, ISO 400	82.86 m flash distance	271.84
GN 58 m, f/2, ISO 100	29 m flash distance	95.14
GN 58 m, f/2, ISO 200	41.01 m flash distance	134.55
GN 58 m, f/2, ISO 400	58 m flash distance	190.29
GN 58 m, f/2.8, ISO 100	20.71 m flash distance	67.96
GN 58 m, f/2.8, ISO 200	29.29 m flash distance	96.11
GN 58 m, f/2.8, ISO 400	41.43 m flash distance	135.92
GN 58 m, f/4, ISO 100	14.5 m flash distance	47.57
GN 58 m, f/4, ISO 200	20.51 m flash distance	67.28
GN 58 m, f/4, ISO 400	29 m flash distance	95.14
GN 58 m, f/5.6, ISO 100	10.36 m flash distance	33.98
GN 58 m, f/5.6, ISO 200	14.65 m flash distance	48.06
GN 58 m, f/5.6, ISO 400	20.71 m flash distance	67.96
GN 58 m, f/8, ISO 100	7.25 m flash distance	23.79
GN 58 m, f/8, ISO 200	10.25 m flash distance	33.64
GN 58 m, f/8, ISO 400	14.5 m flash distance	47.57
GN 58 m, f/11, ISO 100	5.27 m flash distance	17.3
GN 58 m, f/11, ISO 200	7.46 m flash distance	24.46
GN 58 m, f/11, ISO 400	10.55 m flash distance	34.6
GN 58 m, f/16, ISO 100	3.63 m flash distance	11.89
GN 58 m, f/16, ISO 200	5.13 m flash distance	16.82
GN 58 m, f/16, ISO 400	7.25 m flash distance	23.79

Frequently Asked Questions

Frequently asked questions for Flash Guide Number Distance Calculator and its reference values.

How do you calculate flash distance from guide number?

At ISO 100, divide guide number by aperture. For other ISO settings, multiply guide number by the square root of ISO/100 before dividing by aperture.

What does a flash guide number mean?

Guide number indicates flash power for manual exposure planning. A higher guide number generally means the flash can illuminate a subject farther away at the same aperture and ISO.

Why does ISO change effective guide number?

Increasing ISO makes the sensor more sensitive, so the same flash output can expose subjects at a greater distance. The relationship scales with the square root of ISO.

Does this replace test shots and light metering?

No. It is a fast starting estimate for manual flash setup. Modifiers, bounce, zoom head settings, and real scene conditions can change the final exposure.

Methodology and Review

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