# kts or mph

Is the ground speed in kts or mph?

Knots

can you also display mph besides knts because mph is easier to understand any help would be app.? thanks

You can hover over the speeds in knots to see them in Mach. If you want to convert them to MPH, add roughly 15%. For example, 100kts =~ 115mph.

In the future, we’ll add a profile option for units.

For you, maybe. Pilots think in knots (or mach numbers).

Mooneyguy

vossauto said:

can you also display mph besides knts because mph is easier to understand any help would be app.? thanks

dbaker said:

If you want to convert them (knots) to MPH, add roughly 15%. For example, 100kts =~ 115mph.

In most of the aviation world, speeds are indicated in knots and by Mach number. There are some countries that use metric measurements (kilometers per hour and meters for altitude).

As dbaler mentins, just add 15% to get a rough idea of the statue miles per hour. Almost anyone should be able to do this mentally without the aid of a calculator or spreadsheet: Just take 10% of the speed in knots and add one half of that figure. For example, a speeds of 120 knots = 12 plus one of the 10% = 138 miles per hour.

Note that it is NEVER knots per hour. Knots means nautical miles per hour.

I understand about the usage of knots but I’m still mistified as to why AWOS, ASOS and ATIS reports mix English and Metric units. Why are temps in these reports given in Centigrade while visability is reported in miles and sky conditions are reported in feet? Anybody know?

They “only” switched from F to C for METAR/TAF temps about 5 or 10 years ago. Visibility/RVR as well as cloud conditions have stuck to statute miles or feet. Also, remember that the cloud conditions are AGL not MSL.

The reason METARS report temperature in degrees C is because that is the international standard used for temperature in weather reporting and makes more sense since what we care about (in aviation) are freezing temperature (0 deg C) and temperature/dewpoint spread (risk of fog).

The international standard for altitude is feet not meters.

The reason visibility and ceilings are reported in feet/miles is because US approach plates are published with required ceilings/visibility and decision/minimum descent heights in English units (fee/miles). It makes no sense to publish visibility in meters or kilometers when the approach plates are in feet/miles.

Make sense?

Dave

It’s all an issue of legacy standards; there’s no doubt that metric is the superior system. The visibility/ceilings in imperial being justified as reasonable because of approach plates is really just a chicken/egg situation. Temperature/dewpoint spread works the same in F as it does in C. Eventually it will all switch over, it’s just a matter of time.

In fact it was at the same time they switched from SA & FT to METAR & TAF. The METAR/TAF abbreviations assume Celsius (whereas SA/FT assumed Fahrenheit).

As for why the observations are made in statute miles instead of nautical miles, I can only surmise that it is because NWS (and NOAA) set the standards for weather reporting in the US, and they chose statute. NWS has to cater to a much larger number of interests than just aviation and marine, and the truth of the matter is that most people in the US are comfortable and familiar with statue miles.

Except in pilot reports, where cloud conditions are MSL (because that’s what an altimeter reads).

. . . which aren’t METARs or TAFs.

My site is in mph statute miles and I can’t remember how to convert to knots & nm. Can anyone help me on this. Thank you.