corap61•22d agoProlific Poster

Measured a 40 foot run with a tape and got it wrong by 3 inches

I always trusted my tape measure over string lines but last week I checked a 40 foot run with a laser level and found I was off by 3 inches at the end. Turns out temperature changes can stretch a steel tape by about an eighth inch per 100 feet in the sun... now I double check with a string line every time. Has anyone else caught weird tape measure errors on long runs?

3 comments

3 Comments

wade_anderson22d ago

Caught my tape lying to me once on a long run and now I just assume it's plotting against me. How many other people have had a tape just decide to rebel like that?

garcia.cameron22d ago

20 miles in and my Garmin told me I ran a 5:30 mile when I was barely shuffling at like a 9 minute pace. @wade_anderson that's when I knew the tape was definitely out to get me lol

the_cameron22d ago

Oh, temperature stretching is real but that's not quite how it works. Steel tapes are calibrated at 68 degrees and they expand in heat, but it's more like 0.0000065 inches per foot per degree. On a 40 foot run in direct sun at 100 degrees you'd be off maybe 1/16th of an inch, not 3 inches. Something else threw your measurement off.