Decimal separator: dot or comma

What English normally does

Use the decimal point and comma for thousands: 12,345.67.
In scientific/engineering copy that follows SI/ISO 80000-1, prefer thin non-breaking spaces for digit grouping and keep the decimal point: 12 345.67. Never use a comma or a point for grouping in SI style.
Why this matters
Mixed international teams see both styles. 45,321 (EN business style) can be misread by readers used to the decimal comma; 45.321 (comma-countries’ thousands style) looks like forty-five point three two one to English readers.

Green: comma. Blue: point. Image from Wikipedia.

Why this matters
Mixed international teams see both styles. 45,321 (EN business style) can be misread by readers used to the decimal comma; 45.321 (comma-countries’ thousands style) looks like forty-five point three two one to English readers.

Safe, professional choices

For general English deliverables: stick to 12,345.67.
For international/technical documents: use 12 345.67 (thin NBSP) to group digits and avoid ambiguity; stay with the decimal point.
Be consistent within the project and match the client’s existing documents.

Units and spacing

Use a non-breaking space between the number and the unit: 10 630 €, 25 °C, 44 N·m.
Unit symbols are not abbreviations → no periods; no plurals: 5 kg, not 5 kgs.
Prefer kW·h (or kWh) over kW x h.

Examples

Ambiguous: 45,321 (could be forty-five thousand or 45 point 321 to some readers).
Unambiguous SI-style English: 45 321.0.