Measuring off road distances?

[Pan]

Hoping someone could help. I've been building times over distance for a while in running and am doing around 8.30min/mile for what I think is 5 miles. Trouble is..it's all on a trail and I can't really verify the exact distances. I'm looking to get into some more distances over winter and do a competitive half marathon in early spring.
The trail is in a straight line just about, and I measure distance by my pacing. Which could be nonsense. I go out a distance and return the same way.

So....is there an internetty way of more exact measuring using on line maps? Or apps for down loading.The points of ref are landmarks which show up on OS maps for instance. I have strava for cycling but I don't trust it to be that accurate.
The trail is the Longdendale Trail, and my bit follows a disused railway line.

Any ideas would be v gratefully received.

I use mapmyrun on my phone.

Yes, but Mel, I know that the GPS thing isn't that accurate. I use strava, as I say, but some of the readings I know are wrong, from riding distances on my bike and driving them too (to work).
I was wondering about maps which don't rely on actual journeying, but will be able to say 'from there to there IS such and such'. iyswim.

You can try the satellite map on www.walkjogrun.net/. Should be easy enough if you know the route well.

I have a GPS watch and it's pretty accurate.

Walk jog run, seems to work well

I use run keeper and also walkjogrun and have found both to be accurate, checked in the car for road ones! I'd definitely trust them for off road too.

oooh walkjogrun looks good, thanks! Now to work out how it works exactly. thanks v much. Hoping my 5 miles really is 5 miles...

Wow, it works! The first point-to-point followed a road that runs near, but once I'd used the indicator to adjust the route to the trail near by, it recorded it as 2.55 miles from the start, which totalled my current run as 5.1 miles. Which was almost exactly as my pacing estimate.
Many many thanks Eau and everyone else who posted. So I can use this to measure the rest of the trail.
Am extremely grateful.

I use STRAVA app, it's really good.
Tells you your elevation and breaks down the route into sections so you can track each part and see if you are getting faster

Maybe I've been wrong about Strava, Diana. I've used it to track my bike ride to work, which is 13.1miles by road by car trip meter. But Strava on bike said something less. Yes the elevation bit was good - 107 metres which was about right I thought.
A work friend uses it to race himself. But I've no intent on racing to work. Homeward maybe.

walk the whole way with a measuring wheel?

how exact do you think it needs to be, really?

I think most GPS watches are fine for this sort of thing, when I run in a group the miles bleep at slightly different points but it's negligible. Your body will keep the most accurate record.

I use my Garmin at Parkrun and it's only out by a couple of metres, assuming the course is measured accurately.

Yes, yes I was sounding like an obsessive. I just had my pacing to go off, which turned out to be quite accurate in the end! My running buddy is a bit of a smart arse, in a good way....and reckoned the distance was much longer, so I'd wanted to acutual 'prove' something I knew from my body's experience. Quite looking forward to seeing him, with an "in your face!" kind of thing. But in a nice way.