After eight days of testing at the Circuit de Catalunya, Ferrari has emerged as the overwhelming favourites ahead of the first race in Australia. Sebastian Vettel set a 1:16.221 on the final morning of testing, giving him an advantage of 0.340s over Hamilton's teammate using the same compound tyres, Valtteri Bottas.
However, after taking into account fuel loads, engine modes and other variables, Hamilton believes the true gap to Ferrari could be even bigger.
"I'm not quite sure, but I think it is potentially half a second," he said. "We will be analysing a lot from this test and there will be some modifications that we will try to implement for the race, but there is obviously not a lot of time [before Melbourne]. Over the next week we will try to gain another tenth at least in our understanding of the car.
"The car is old now and worn and torn, so we will have new components and all of that stuff will come along. It will be interesting. So Melbourne will be the first time you get a sight of it and then it will be a good four races before you know just where you stand."
But ahead of the season opener, Hamilton doubts Mercedes can do enough to make big gains in the two weeks before the first practice session in Melbourne.
"I've no reason to expect that [gap] to come down," he said. "Testing you have to take with a pinch of salt. You could get there and it could be bigger, you could get there and it could be less, you could get there and it could be equal.
"There's no way when you're looking at GPS to say what fuel load they're on and what engine mode they're on. They're faster on the straights than us for example. Now is that because they have their flexi-wings that they've had in the past that drops drag? Or are they more turned up than us or are they just more efficient and just have less drag than us in general? Or are we heavier? So we have no idea.
"Of course naturally we hope that it's definitely not bigger than what we might see now, we hope that it's better, but we can't bank on that. So we just have to work towards trying to close that gap that we think might be there, or is there."
Hamilton suspects Red Bull is also in the mix and believes the midfield teams will be much closer to the top three.
"I think it is the three teams [at the front], but also the teams at the back have closed up as far as I'm aware," he said. "The whole pack has closed up, I don't know which team is fourth currently, but they are a lot closer than they were before. There was like a second gap before but now they are within half a second or maybe less, which is awesome."
New regulations have presented a new challenge to teams this year, essentially restricting the ease with which they can manipulate the airflow around the front tyres. That has a knock-on effect on the way the rest of the car produces downforce, and recovering that aero performance has been one of the key battlegrounds over the winter.
It seems Ferrari and Mercedes have come up with very different ways of approaching that task and have both tested different styles of front wings. Switching from one style to another would require a major rethink of the car, but Hamilton said it is still too early to say if one team has got it right and the other has got it wrong.
"Currently we don't hold that [concern], but of course there's a question mark over whether they have the right philosophy or whether we have the right philosophy," Hamilton said. "Time will tell. The guys, the engineers, will be analysing both for sure, that's what they do.
"I'm sure Ferrari as a team, probably all the other teams do the same thing, they will look at the other options. But we know the car has not been performing optimal in these two weeks. We might tweak it but that does take time, so I don't have an answer for you about when that will be."