How long does light take to cross that?

Light covers 30 cm in a nanosecond. Grace Hopper used to hand out 30 cm wires to make the point.

The distance Unit

Almost exactly a to the Moon

384,400 km is further than 2 of the 7 references on this page.

Reference figures are measurements and are rounded; the unit conversion behind them is exact.

Every reference on this page, with its size and its ratio to your number
Reference	Size	Yours ÷ theirs	Note
one light-nanosecond	0.0003 km	1,282,188,125×	About one foot
once around the Earth	40,075 km	9.59×	Light does this 7.5 times a second
to the Moon	384,400 km	1×	1.28 light-seconds
to Mars at closest	54,600,000 km	1/142	About 3 light-minutes
to the Sun	149,597,871 km	1/389	8.3 light-minutes
to Neptune	4,500,000,000 km	1/11,707	4.2 light-hours
to Proxima Centauri	40,000,000,000,000 km	1/104,058,273	4.25 light-years

Light takes 1.28 seconds to reach the Moon, so a conversation with an astronaut there has a 2.6-second round trip.
The Sun you can see left it 8 minutes and 20 seconds ago. If it went out, we would not know until then.

Frequently asked

Exactly 9 460 730 472 580 800 metres — an exact number, because both the speed of light and the Julian year are defined values.

Because the numbers in metres are unusable, and because the unit carries information: looking four light-years out is looking four years back.