Horses come in a variety of shapes and sizes. If a horse is exceptionally broad in the back it may be necessary to buy the next size up in relation to its height. Alternatively, it may be necessary to look at several different
styles. When purchasing your rug check with your retailer that in the event of that particular model not fitting your horse, he will exchange it. When trying the rug on the horse protect it by fitting it over a summer sheet or something similar so that you can return it clean and suitable for re-sale.
It is essential that a rug should fit well on the withers and shoulders so
that the horse can move freely underneath the fabric without the rug
slipping back. If this happens the rug is put under strain and can cause sore areas. Once you have ascertained that the rug fits well around the neck, pull the rug into position along the horse’s back so that the coat lies flat. With rugs using leg straps- take the left leg strap, pass between the hind
legs and fasten it on the left-hand side. Take the right leg strap, pass it between the hind legs and through the loop made by the first strap and fasten to the right hand side. Adjust the leg straps equally until there is room for the width of one hand (4-5") between the leg straps and the horse’s thigh. This is to allow freedom of movement.
The leg straps are linked to prevent rubbing and act with each other to pull the rug into place. When the horse is grazing, the leg straps should be close to its thighs to keep the rug in position. If you fit the rug as we have described here it will displace very little through movement and rolling.
If the leg straps are too loose, the rug will slip.

When fitting a rug with cross surcingles care should be taken to ensure that the straps of the cross surcingle cross in the centre of the horse’s belly well forward of the horse’s stifle. i.e. so that the crossed straps are on the roundest part of his body. Again, there should be a hands breadth between the straps and the horse.