By Ron Dalby
Driving to Alaska means you have to first drive through a large part of Canada, a real treat. However, Canada is a separate country with differing customs, and, for about 40 years now, uses the kilometers of the metric system instead of the miles that Americans are so familiar with.
The basic thing to remember is that kilometers are shorter than miles so there are more of them. The ratio is approximately 100 kilometers equals 60 miles.
Decades ago my father taught me a fairly simple way to figure things out in my head. His words were, “Multiply the number of kilometers by six and drop the last digit.” For example, if a sign indicates your destination is 350 kilometers away, multiplying by six yields 2,100. Drop the last digit and you have 210 miles, a figure that is correct within a kilometer or two. Or if a speed limit sign in a school zone says 30 KPH, this formula will yield 18 MPH.
Ron Dalby is the author of Guide to the Alaska Highway.
##RVDT2044
Great! I can remember that…not that I plan to need it but still good to know!
Great rule of thumb! Thank you! However both speedometers (RV and towed Jeep) display both mph and kph. The settings of both allow one to choose kilometers OR miles as the default distance measurement standard.
Many US speedometers include both mph and kph scales. If you have a vehicle with a digital speedometer, odds are good that there is a switch to display in either scale. Use a GPS system? Most automatically shift between US and metric based on location and show current speed and distance to destination.
For those without, while the 6/10 guide might be ‘good enough’, a more exact ratio is 5/8. So 50mph is 80kph. In which ever system you need to convert, some simple fractions against those two values also gives you the other. So for slower speed zones, 25mph is 40kph; half-way 25 & 50 is 37.5 (just under 40mph) which is also half-way between 40 & 80 or 60kph.
A common open highway speed is 100kph, which is just a bit over 60mph. Frankly, I rarely drive faster than that while towing.
I think the “good enough” rule is a better choice.
And, if you want a gauge for temperature, Cº x 2 -10% +32 = Fº. Double it, subtract 10% and add 32. Example: 20º C x 2 = 40º, 40 – 4 = 36º, 36 + 32 = 68º F. Had to do this all the time in aviation — becomes easy in your head after a few times.
Now, if my aged brain could only remember the formula!
Before you go to Canada, measure the height of your rig, and convert it to meters. Overpasses in Canada show the heights in meters. A meter is about 39 inches. Simply ask your Siri, or Alexa to convert your rig height and write it down.
Cool!!
Rather than trust my math skills, I put a yellow post-it note on the dash near the speedometer to translate mph to kph at a glance.
Since most US speedometers have a dual scale, with kph in smaller numbers on an inner circle, just calculate distances by comparing the two scales; i.e., 62 mph = 100 kph, thus 62 miles = 100 km (or vice-versa). This only works, of course, while you’re driving and have a speedometer handy to look at.
The author has provided a great tip, and although I previously used the somewhat hard to see inner ring on the speedometer, my current vehicle has a digital speed display that switches from MPH to KPH at the push of a button. No math and no straining to see and absolutely accurate.
Some vehicles, like mine, won’t let you change MPH to KPH or back unless the vehicle is stopped.
you have to STOP at the border so change it then…..it should not be a surprise you are at the boarder all of a sudden…
Hi, Dan. Impavid didn’t say he didn’t do that. He merely stated that some vehicles require you to be stopped to change it. He’s crossed the border many, many times. Just sayin’. Have a great day. 😀 –Diane at RVtravel.com
An easier way to roughly convert a distance or speed from measurement in kilometers to measurement in miles is to utilize this much easier to remember method:
simply ..’CUT THE GIVEN NUMBER IN HALF AND ADD TEN PERCENT OF THE ORIGINAL GIVEN NUMBER’
e.g as pertains to speed, say 100 kph to mph by applying the above method..100/2 = 50 then adding 10% =10 thus the speed limit computes to 60mph ( 50 + 10 =60)
e.g.. as pertains to distance say, 350 kilometers…. 350/2 =175 plus 10% =35 calculates to 175+35 =~210 miles
The same method works for either speed or distance. SO MUCH EASIER and FASTER than multiplying by .6 etc. etc. blah blah blah!
Now to convert from miles to kilometers it’s just a tad more mind-taxing but not too difficult. How?
Simply take the original mlles or MPH figure and add 75% (or 3/4 of the original figure.
e.g for mph to kph say, for example sake 60mph… so, 60 plus 45 (75% or 3/4 of 60) adds up to 105kph. Not exact, but not far enough off to win you a speeding ticket in most of Canada, even on a bad day 😉
e.g. using the distance in the first example above, 210 miles to kilometers calculates like this 210 + 157.5 (3/4 or 75% of 210) = 367.5. This calculation is a bit further off, but hey!… when you’ve already driven 350 kilometers, will another 17.5 REALLY be that more intolerable?? 😉
Happy Trails!
Of course unless you’re driving a vehicle that is over 50 years old you could just look at the speedometer since they have displayed mph and kmh for many years. If you’re driving a relatively newer vehicle there is probably a selector button on the dash that will change the read outs to killermeters. You have to be careful of those. Lol
Wow, super cool, even I can remember that! Thanks!
We’ve lived in Europe where Kilometers are also used. We just multiply the Kms by .6 and it works out fine. To reverse and go from miles to Km you have to multiply the miles by 1.65 and that gets you pretty close. Each Km is .6 of a mile or just over half a mile. 2 Kms is 1.2 miles. Isn’t math fun?
I use this rhyme to help remember the Metric temperature scale:
30 is hot, 20 is nice, 10 is cool and Zero is ice.
When we went through Canada in 2017 and took the Alaska Highway as soon as we entered Alberta I set our Garmin to kilometers and used it as our speedometer. Worked great.
Um… “the ratio is approximately 100km:60mi,”… or 0.6, or multiply by 6/10 or, multiply by 6 and divide by 10… how is this a trick? I’m more likely to forget the 1.6 and 0.6 factors than how to do basic math from there.
Also, most speedometers have dual scales, and most GPSes auto convert units by location…
If you have trouble remembering 6’s, track runners/parents might remember the 4s of a school track being 1/4mile and 400meters.
Instead of multiplying by 6 THEN dropping the last digit, it would be easier to drop the last digit first THEN multiplying by 6. So 350KM would then be 35 multiply by 6 = 210 miles.
As far as speed goes, Wolfe is correct in that the speedometers show both speeds.
But the formula works well with figuring out how far you want to travel, say to pre-plan your trip and knowing where to plan your fuel stops at since you probably already know how far in miles you want to go.