I was curious about that a while ago and found these charts.
From the American University Center of Provence
CEFR
ILR
ACTFL
A1
0/0+
NL, NM, NH
A2
1
IL, IM
B1
1+
IH
B2
2/2+
AL, AM, AH
C1
3/3+
S
C2
4/4+
D
From Heritage Canada
CEFR
ILR
ACTFL
NB OPS[28]
CLB
PSC PSC[29]
A1
0/0+/1
Novice (Low/Mid/High)
Unrated/0+/1
1/2
A
A2
1+
Intermediate (Low/Mid/High)
1+/2
3/4
B
B1
2
Advanced Low
2+
5/6
C
B2
2+
Advanced Mid
3
7/8
C1
3/3+
Advanced High
3+
9/10
C2
4
Superior
4
11/12
4+/5
CEFR is a European standard.
So basically a 1+ is an Intermediate High, but that's also just for Speaking. Not sure what the exact test would be like, but I took a test for ILR Speaking 3 and had three basic questions that I had to answer with 90+ second responses. They were all simple opinion-based questions and didn't require any specific technical knowledge in the language. Basically small talk.