How to Calculate 1/4-Mile Results
Here is how you can determine your car's overall performance without ever needing to test on a dragstrip. Your car's weight number and and horsepower number are what's needed, but those are not the only figures needed.
Plenty of these calculators exist, but they're mostly sixth-grade level estimates without a hint of traction, gearing, torque, drag coefficient and other aero factors, etc.
I find two of these calculators to be the most accurate. Both work best on cars with 300-600hp. It won't work on extremely high-performance cars like a Bugatti Chiron or Koenigsegg Regera (~1500hp).
RobRobinette represents numbers posted in American magazines subtracting the one-foot rollout: (1/60)^1*[60' ET](10). Magazines like Motor Trend, Car and Driver, and Road & Track tend to use these measurements. Requires curb weight to be inserted in lb = kg/.453592.
TorqueStats represents numbers posted in magazines from around the world with somewhat dated tactics: lack of launch control, use of the classical "bhp" rating, and results performed on a standing surface. Very popular magazines from the UK (Autocar, EVO, Top Gear, etc.), Germany (AMS, Auto Bild, Sport Auto, etc.), and Australia (CarSales, Motoring, WhichCar, etc.) tend to use these measurements. Requires kerb weight to be inserted in kg = lb/2.204623.
For modern vehicles (2004-2005+)
Naturally aspirated and supercharged cars should have their power numbers inserted in "flywheel" horsepower. Turbocharged and electric cars should have their power numbers inserted in "wheel" horsepower — i.e., multiplied by 1.14 on RobRobinette and 1.2 on TorqueStats.
If you're into really optimistic figures on TorqueStats, multiply the power figure by 1.2 (twice, for turbos). This will actually put your car into measurements that most magazines use today.
If you have a manual transmission or a really old-school automatic (such as a 4- or 5-speed auto), I highly suggest using TorqueStats.
If you have a dual-clutch transmission or a super-tech-savvy automatic (like an 8-, 9-, 10-speed auto), I highly suggest using RobRobinette.
For older vehicles (pre-2004/2005)
Power figures for British cars rated in the "brake horsepower" formula (as opposed to American or European hp) should be multiplied by 0.86 on RobRobinette — but retain the same bhp figure on TorqueStats.
Most non-British naturally aspirated and supercharged cars' power figures should remain flywheel on RobRobinette, but multipled by 1.2 on TorqueStats. Turbocharged cars, like naturally aspirated and supercharged cars, should have power figures multiplied by 1.2 on TorqueStats; but they should also have hp figures upgraded to "wheel" numbers.