I ordered this onesie from the Deal Rack through Amazon.  I ordered the 12-18 months size for my 12 month old, who is in the 50th percentile for height/weight.  This was nowhere near big enough for him.  It's similar to 6 month size clothing from other brands.  Now I'm out the cost of shipping both ways when I return it.  I'd either order a size you think will be absurdly too big and hope for the best, or better yet, choose another brand.