Gas switch calculator

Calculate the partial pressure differences between two gases for different ambient pressures

From Gas

O2:
HE
N2: 40

To Gas

O2:
HE
N2: 50

Depth
[m]		ppO2
[bar]		ppN2
[bar]		ppHe
[bar]		O2/HeDensityIANTD 5% rule
6from
to
diff		1.30
0.80
0.50		0.14
0.80
0.66		0.16
0.00
0.16		81/10
50/0
 		2.06
2.14
 		41% N2 incr
10% He drop
2% N2 incr max
10from
to
diff		1.30
1.00
0.30		0.33
1.00
0.67		0.37
0.00
0.37		65/19
50/0
 		2.34
2.68
 		34% N2 incr
19% He drop
3.8% N2 incr max
20from
to
diff		1.30
1.50
0.20		0.80
1.50
0.70		0.90
0.00
0.90		43/30
50/0
 		3.02
4.02
 		23% N2 incr
30% He drop
6% N2 incr max
30from
to
diff		1.30
2.00
0.70		1.27
2.00
0.73		1.43
0.00
1.43		33/36
50/0
 		3.7
5.36
 		18% N2 incr
36% He drop
7.2% N2 incr max
40from
to
diff		1.30
2.50
1.20		1.74
2.50
0.76		1.96
0.00
1.96		26/39
50/0
 		4.38
6.7
 		15% N2 incr
39% He drop
7.8% N2 incr max
50from
to
diff		1.30
3.00
1.70		2.21
3.00
0.79		2.49
0.00
2.49		22/42
50/0
 		5.07
8.04
 		13% N2 incr
42% He drop
8.4% N2 incr max
60from
to
diff		1.30
3.50
2.20		2.68
3.50
0.82		3.02
0.00
3.02		19/43
50/0
 		5.75
9.38
 		12% N2 incr
43% He drop
8.6% N2 incr max
70from
to
diff		1.30
4.00
2.70		3.15
4.00
0.85		3.55
0.00
3.55		16/44
50/0
 		6.43
10.72
 		11% N2 incr
44% He drop
8.8% N2 incr max
80from
to
diff		1.30
4.50
3.20		3.62
4.50
0.88		4.08
0.00
4.08		14/45
50/0
 		7.12
12.06
 		10% N2 incr
45% He drop
9% N2 incr max
90from
to
diff		1.30
5.00
3.70		4.09
5.00
0.91		4.61
0.00
4.61		13/46
50/0
 		7.8
13.4
 		9% N2 incr
46% He drop
9.2% N2 incr max
100from
to
diff		1.30
5.50
4.20		4.56
5.50
0.94		5.14
0.00
5.14		12/47
50/0
 		8.48
14.73
 		9% N2 incr
47% He drop
9.4% N2 incr max

Color visualization is for partial pressure difference only.
Green: Partial pressure difference is below 0.5
Orange: Partial pressure difference is between 0.5 and 1.0
Red: Partial pressure difference is above 1.0

IANTD 5% rule aka IANTD rule of fifth

The 5:1 ratio indicates that a diver should not switch to a gas that has a helium drop of 5% (actual percent by volume) for every 1%(actual percent by volume) increase in nitrogen content.
[Tom Mount, Joseph Dituri: Exploration and Mixed Gas Diving Encyclopedia (The Tao of Survival Underwater)]

This can be rephrased into: `"`Limit your rise in N2 to one fifth of the drop in Helium as you ascend.`"`

This calculation might be incorrect and / or contain bugs. Taking this calculations for real might kill you.
Do not rely on this tool for your dive planning.
Do your own calculations.

You are most welcome to check the source code on GitHub and report bugs if you find some.

Copyright Cornelius Schmale 2025