Prado ticket lines?

Well, probably shorter than they would be on a weekend, but they still get lots of people. My impression is that May is field trip month and you see lots of school children of all ages. However, this museum is amazing and handles the crowds well.

In Madrid, many of the museums have free entry times...

Prado (€14) Tue-Sat 1000-2000, Sun 1000-1900, Closed Mon (Free after: 1800 Tue-Sat, 1700 Sun)
Reina Sofia (€8) Mon-Sat 1000-2100, Sun 1000-1900, Closed Tue (Free after: 1900 Mon-Sat, 1330 Sun)
Thyssen Bornemisza (€10) Tue-Sun 1000-1900, Mon 1200-1600 (Free: Mon 1200-1600)
Museo Sorolla (€3) Tue-Sat 0930-2000, Sun 1000-1500, Closed Mon (Free: Sunday, Sat after 1400)
Museo Lazaro Galdiano (€6) Mon-Sat 1000-1630, Sun 1000-1500, Closed Tue (Free: last hour of every day)
Museo Cerralbo (€3) Tue-Sat 0930-1500, Sun 1000-1500, Closed Mon (Free: Sunday, Sat after 1400)
Museo de America (€3) Tue-Sat 0930-1500, Sun 1000-1500, Closed Mon (Free: Sun 1000-1500)
Real Academia de Bellas Artes (€6) Tue- Sun 1000-1500, Closed Mon, (Free: Wed)

We were there at the end of October/2016, on a RS tour. The very last tour of the season I believe, and there were school kids there then, and there were people lined up at 2pm. Not a longline, by any means and it moved fast and also some school groups. I have to say, which is why I am responding to this injury, that it was the most amazing gallery we have ever been in and well worth the time in line. I would gladly go back and stand in line to see this beautiful place. First time we had a guide alsom in a gallery, so worth it, was amazing,

Ps, sorry about the typos!

We were there last May, and I honestly don't remember the lines being bad at all.

I don't want to stand in line at all. Can tickets be purchased online?

By not too bad, I mean we waited a few minutes at most.

If you're there early in the day, it's probably okay. The line for the security check may be a bit slow if you end up behind a group, but there's no way to avoid it.

What I did was buy a ticket towards the end of the day, when there were no lines, then go two days later (so I had my ticket in hand for the day I wanted to go). You do have to specify the day you want the ticket for, but they will sell them in advance.

If you are going to one or both of the other Art museums, you can buy a combo ticket where it may be less busy, I bought mine at the Thyssen-Bornemiza. I would assume there will be a line, when I was there in February, it was a massive line, on a Friday I believe. Even with a ticket, either advanced or combo, there may be a line at that entrance (ticket holders use a separate entrance), since everyone has to go through Security.

I would get there at 0945, if paying, or at 1745 (for the free time) to queue for security checks.

I walked past there this morning, and at 10:00 a.m. there was a line maybe 50 people long. When I walked by again around 2:30 there was no line at all. And today is a Saturday of a holiday weekend.

I think the standout observation made by many, borne out by Nancy's comment, is that the Prado seems very efficient at dealing with the large volume.

We bought the three museum ticket thinking to skip lines but at the Prado we had to stand in line to exchange it for a ticket so we could have bought the very cheap senior ticket instead. There are several entrances at the Prado and some have shorter lines than others. We were there in May and the line was not a problem; we were sorry we had bought the three ticket deal as the only place it helped skip lines was at the Thyssen, where they just took the coupon.