[tobytoby]

I know there is a formula/method for weighing pigs with a tape, but what about weighing my sheep?
There isn't anyone near me that i know who has scales, that i could borrow.

[Foobar]

There is, but it only works if the animal has no wool , so it's not really viable.
I think there are other threads on here about homemade sheep scales...

[Fleecewife]

Is this to know their exact weight for drug dosing, or to see if they are the correct weight for slaughter?   We never weigh ours before slaughter, but we do assess their body condition score.  This is because different breeds have different conformation, so some are smaller or larger overall then others, some have lighter or heavier bones, some have a different meat:bone ratio.  Consequently their ideal slaughter weight will be different for many breeds, at least for home consumption.   I believe butchers want all their lambs to weigh 40kgs - not possible in some breeds 
 
Estimating your sheeps weight is very unreliable - as Young Farmers 'guess the weight of the ewe' competitions have shown.  You would have to lift many sheep and estimate their weight, then weigh them to see the actual weight.   It really is far better to actually weigh them, at least the largest and the smallest.  You can easily make a portable weighing rig to use in the field, if you can find a suitable hanging scale.

[SallyintNorth]

Up here, butchers want larger lambs - 24-26kg deadweight, which with a good conformation Texel type will be 45-50kgs liveweight.  The most popular lambs in the auction ring are good conformation Texel types which will kill out at 20-21kgs (so around 38-40kgs liveweight) as this is what the supermarkets want to buy.  Smaller yet for the export market.

You won't know until you have a few of yours away, what conformation they have and what killout %age you get.  On the moorland farm, our grass-reared Texels-out-of-mules would be mostly R3L (bog standard, absolutely fine, conformation - but not in the bonus bracket) and would kill out at about 40-44% of their liveweight.  Here, BH produces top spec (conformation E2, E3L, U2, U3L) Texel types which kill out at around 50% or better.

You can't much influence the E, U or R by feeding, it comes mainly from the breeding.  (Although an unfit lamb will likely be a point lower than its potential.)  You can make them too fat (anything over 3L is too fat) with food, or too thin (1 is too thin) with lack of feeding. 

A lamb is ready to slaughter when it is fit - condition 2 or 3L - irrespective of its weight.  If you send them away because the weight is right but they haven't yet achieved fitness (CS 1) you won't get as much for them, and if you keep them longer hoping to get them heavier they'll just slab on the fat, be condition score 3H, 4 or more, and again you won't get as much for them.

So if it's about deciding if they're ready to butch, learn to condition score.  Eblex have good leaflets, and cracking hands-on materials if you can find them at a show.

[Big Light]

 if you can, stand on your domestic human weighing scales holding the animal and deduct your own weight ( need hard surface or sheet of wood / slab if in a field)