Top Speed Calculator
Estimate a car’s aerodynamically-limited top speed from its horsepower, drag coefficient and frontal area.
How it works
Aerodynamic power P = ½·ρ·Cd·A·v³ · Solve for v = (2P ÷ (ρ·Cd·A))^(1/3), with ρ ≈ 1.225 kg/m³ and P in watts
At top speed a car’s available power is entirely consumed pushing air aside, so the maximum velocity is set by the balance between engine power and aerodynamic drag. Because drag power rises with the cube of speed, going faster gets dramatically harder — doubling top speed needs eight times the power. This model uses the wheel power (crank power times drivetrain efficiency), the drag coefficient and frontal area, and ignores rolling resistance, wind and gearing, so it slightly overestimates the true limit for cars that run out of gearing before they run out of power.
Worked example
A 300 hp car at 85% efficiency delivers about 190,000 W to the wheels. With Cd 0.32 and 2.2 m² frontal area, v = (2 × 190,000 ÷ (1.225 × 0.32 × 2.2))^(1/3) ≈ 76 m/s, which is about 274 km/h or 170 mph.
Frequently asked questions
Why does top speed depend on the cube root of power?
Drag power grows with the cube of speed (P ∝ v³), so to solve for speed you take the cube root of power. This is why big power increases yield only modest top-speed gains once a car is already fast — the last few mph cost enormous amounts of power.
How do I find my car’s frontal area?
A good approximation is height × width × 0.85 (the 0.85 accounts for rounded edges and the gap under the car). A typical sedan is around 2.1–2.3 m²; SUVs and trucks are larger, which is a major reason they have lower top speeds for the same power.
Why might my real top speed be lower?
The estimate ignores rolling resistance, gearing limits, rev limiters, wind and the fact that few cars are geared to reach their theoretical drag-limited speed. Many cars hit the rev limiter in top gear well before the aerodynamic ceiling.
Related calculators
Educational estimate — real figures vary by vehicle, load, conditions and manufacturer specs. Always follow your owner’s manual.