Given a Bram Stoker-derived "ten times stronger than an ordinary human", a vampire about the mass of an average human (67 kg), with about ten times the leg strength of an average human (about *83 kg per leg), so 830 kg per leg, meaning a thrust-to-mass ratio of ~12.39x.
We then plug it into the handy Quadratic Formula, first intercept form:
Remember to put the square root in... *Cough*
T1 = (-B - (B*B - 4*A*C)^0.5) / (2 * A)
A = -9.8 / 2 = -4.9;
B = 12.39; Assuming a more realistic 70% of this number before we leave the ground gives us 8.673. We'll just call that 8.7 m/s
C = 0
T1 = ((-8.7) - (8.7^2 - 4*(-4.9)*0)^0.5) / (2 * -4.9)
T1 = ((-8.7) - (8.7^2)^0.5) / (2 * -4.9)
T1 = ((-8.7) - 8.7) / (2 * -4.9)
Run through calculator (Windows Calc doesn't like it, so manually):
T1 = ~1.78 seconds
Checked with website quadratic calculator:
T1 = ~1.78 seconds
From there, some linear position:
First, *Cough* half the time taken is half-way through the jump, and thus its zenith.
T = 1.78 / 2 = 0.89
P2 = P1 + V*T + 0.5*A*T*T
P2 = 0 + 8.7*0.89 + 0.5 * -9.8 * 0.89 * 0.89
3.86 meters straight up... Yeah, I can see how vampire movement could be mistaken for flying!
With a running pace of a footstep or two per second, a vampire would be a literal blur.
And now you know. And knowing is half of figuring out which hardwoods can make viable bullets.
Which means a vampire would have an eerie, gliding movement, even at a full dash, because jumping in a battle = dead, as **any martial artist, historian, or soldier would tell you. So feet on the ground, and a lot less bobbing movement, because pushing down like you would if alive is going to send you several inches up. Or in other words, an awkward hop-stumble.
* I had more precise numbers, at one point. Also, RPG design and development.
** Cannot guarantee. Not an expert on any of those. Have done karate.