For NDT applications there are mainly two group of standards for focal spot measuring:
EN 12543 parts 1 to 5
and
ASTM E1165 (pinhole method - similar to EN12543-2) and ASTM E2903 (edge method - similar to EN12543-5).


EN 12543 is a series of European Standards for focalspot measurement, originally from 1999, updated in 2012:
EN 12543-1, Non-destructive testing - Characteristics of focal spots in industrial X-ray systems for use in nondestructive testing - Part 1: Scanning method
EN 12543-2, Non-destructive testing - Characteristics of focal spots in industrial X-ray systems for use in nondestructive testing - Part 2: Pinhole camera
EN 12543-3, Non-destructive testing - Characteristics of focal spots in industrial X-ray systems for use in nondestructive testing - Part 3: Slit camera radiographic method
EN 12543-4, Non-destructive testing - Characteristics of focal spots in industrial X-ray systems for use in nondestructive testing - Part 4: Edge method
EN 12543-5, Non-destructive testing - Characteristics of focal spots in industrial X-ray systems for use in nondestructive testing - Part 5: Measurement of the effective focal spot size of mini and micro focus X-ray tubes
As far as I know there will be a revision soon - Part 1 will be skipped, Part 2 will be aligned with ASTM E1165-12 and a new part is discussed for sub-5µm focal spots; the user method in E1165 is also in discussion for EN.

ASTM E1165 was first published in 1987 from ASTM Committee E-7 in Subcommittee E07.01. There was a major update in 2012 when the pin hole method was aligned to EN 12543-2; a new method for evaluation was introduced (Integrated Line Profiles) and a table for focal spot classes introduced (Table 3). Additionally an annex A1 with an alternate focal spot measurement method for end users is included that end users can measure the unsharpness due to the focal spot with a simple hole penetrameter - this method shall be also included in the EN 12543 in future. Finally a test report in accordance with ASTM E691 was done to give a Precision and Bias statement. For details around this first digital method see paper
“New measurement methods of focal spot size and shape of X-ray tubes in digital radiological applications in comparison to current standards”, Klaus Bavendiek, Uwe Heike, Uwe Zscherpel, Uwe Ewert and Adrian Riedo, WCNDT 2012, Durban, South Africa

ASTM E2903 was first published one year after the major update of E1165 in 2013. It is based on the European standard, EN 12543–5, and intended for the measurement of effective focal spot dimensions from 5 up to 300 μm of X-ray systems up to and including 225 kV tube voltage, by means of radiographs of edges. New in E2903 is the use of digital techniques (EN is film still). Technical details on the transfer to the digital method can be found in the paper
“Measuring microfocal spots using digital radiography”, Fry, Ewert, Gollwitzer, Neuser, and Selling, Materials Evaluation, Vol 70, No.8, August 2012, p. 981ff.

As announced 6 years ago the EN 12543 war updated and now replaced by ISO 32543.
In ISO 32543-1, the pin hole method permits the measurement of focal spot shape and focal spot sizes ≥ 100 μm. This is former EN 12543-2 and similar to ASTM E1165/26.
The edge measurement method of ISO 32543-2 uses the edge method with hole or disk type test objects and is intended as a user method for measurement of effective focal spot sizes of nano-, micro-, mini- and macro- (standard) focus tubes; the new method is similar to the annex of ASTM E1165/26.
ISO 32543-3 covers the measurement of the effective focal spot size of mini- and microfocus X-ray tubes from 5 μm to 300 μm. This is former EN 12543-5 and similar to ASTM E2903.

Two further parts are on the way ...