The electromagnetic form factors of charged and neutral kaons are strongly constrained by their low-energy singularities, in the isovector part from two-pion intermediate states and in the isoscalar contribution in terms of $$\omega $$
ω
and $$\phi $$
ϕ
residues. The former can be predicted using the respective $$\pi \pi \rightarrow {{\bar{K}}} K$$
π
π
→
K
¯
K
partial-wave amplitude and the pion electromagnetic form factor, while the latter parameters need to be determined from electromagnetic reactions involving kaons. We present a global analysis of time- and spacelike data that implements all of these constraints. The results enable manifold applications: kaon charge radii, elastic contributions to the kaon electromagnetic self energies and corrections to Dashen’s theorem, kaon boxes in hadronic light-by-light (HLbL) scattering, and the $$\phi $$
ϕ
region in hadronic vacuum polarization (HVP). Our main results are: $$\langle r^2\rangle _\text {c}=0.359(3)\,\text {fm}^2$$
⟨
r
2
⟩
c
=
0.359
(
3
)
fm
2
, $$\langle r^2\rangle _\text {n}=-0.060(4)\,\text {fm}^2$$
⟨
r
2
⟩
n
=
-
0.060
(
4
)
fm
2
for the charged and neutral radii, $$\epsilon =0.63(40)$$
ϵ
=
0.63
(
40
)
for the elastic contribution to the violation of Dashen’s theorem, $$a_\mu ^{K\text {-box}}=-0.48(1)\times 10^{-11}$$
a
μ
K
-box
=
-
0.48
(
1
)
×
10
-
11
for the charged kaon box in HLbL scattering, and $$a_\mu ^\text {HVP}[K^+K^-, \le 1.05\,\text {GeV}]=184.5(2.0)\times 10^{-11}$$
a
μ
HVP
[
K
+
K
-
,
≤
1.05
GeV
]
=
184.5
(
2.0
)
×
10
-
11
, $$a_\mu ^\text {HVP}[K_SK_L, \le 1.05\,\text {GeV}]=118.3(1.5)\times 10^{-11}$$
a
μ
HVP
[
K
S
K
L
,
≤
1.05
GeV
]
=
118.3
(
1.5
)
×
10
-
11
for the HVP integrals around the $$\phi $$
ϕ
resonance. The global fit to $${{\bar{K}}} K$$
K
¯
K
gives $${{\bar{M}}}_\phi =1019.479(5)\,\text {MeV}$$
M
¯
ϕ
=
1019.479
(
5
)
MeV
, $${\bar{ \varGamma }}_\phi =4.207(8)\,\text {MeV}$$
Γ
¯
ϕ
=
4.207
(
8
)
MeV
for the $$\phi $$
ϕ
resonance parameters including vacuum-polarization effects.