Enter the wheel horsepower and select the drivetrain of the car to determine the brake HP (crank HP) from WHP.
Drivetrain Loss Table
| Drivetrain | Loss | Efficiency | Typical Notes |
|---|---|---|---|
| FWD Manual | 10% | 0.90 | Usually among the lowest drivetrain losses due to a simpler layout and lower parasitic loss. |
| FWD Automatic | 12% | 0.88 | Slightly higher losses than manual FWD because of the automatic transmission and torque converter effects. |
| RWD Manual | 13% | 0.87 | Moderate loss from the transmission, driveshaft, and rear differential. |
| RWD Automatic | 15% | 0.85 | A common rule-of-thumb estimate for many rear-wheel-drive street cars with automatic transmissions. |
| AWD Manual | 18% | 0.82 | Higher loss because power goes through additional differentials and transfer components. |
| AWD Automatic | 20% | 0.80 | One of the most common broad estimates used for AWD cars on WHP to crank HP conversions. |
| 4WD Truck / SUV | 22% | 0.78 | Heavier rotating assemblies, larger driveline parts, and truck-oriented systems can raise losses further. |
| Heavy 4WD / Performance AWD | 25% | 0.75 | Useful as a conservative estimate for very heavy, complex, or high-loss driveline setups. |
These are rule-of-thumb estimates, not fixed mechanical constants. Actual drivetrain loss can vary based on transmission type, dyno type, tires, fluids, and vehicle setup.
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What Is WHP?
WHP means wheel horsepower. It is the amount of horsepower that actually reaches the wheels after the engine’s power passes through the drivetrain. This is the number most commonly measured when a car is tested on a chassis dyno.
Wheel horsepower is often more useful than advertised horsepower because it reflects how much power the vehicle can actually put to the ground. Two cars may both be rated at 400 horsepower from the factory, but one might make 330 WHP while the other makes 360 WHP depending on drivetrain layout, transmission type, tires, drivetrain efficiency, and dyno conditions.
WHP is especially popular in performance tuning because it shows the real-world result of modifications. If a car starts at 280 WHP and makes 330 WHP after a tune and exhaust upgrade, the owner can see that the car gained about 50 horsepower at the wheels. That is usually more meaningful than estimating engine output alone.
What Is HP, BHP, or Crank Horsepower?
HP usually means horsepower, but in car discussions it often refers to crank horsepower or brake horsepower. BHP stands for brake horsepower, which traditionally means the horsepower measured at the engine using an engine dynamometer. In everyday automotive language, BHP and crank HP are often used almost interchangeably.
Crank horsepower is the engine’s power before drivetrain losses. This is usually the number advertised by vehicle manufacturers. For example, if a car is listed as having 450 horsepower, that number typically refers to engine output, not the amount of power measured at the wheels.
The difference matters because the drivetrain consumes some of the engine’s power. The transmission, clutch or torque converter, driveshaft, differential, axles, bearings, wheels, and tires all require energy to rotate. That lost energy is why wheel horsepower is lower than crank horsepower.
WHP vs HP: What Is the Difference?
The difference between WHP and HP is where the power is measured.
WHP is measured at the wheels. HP or BHP is measured or estimated at the engine. WHP is lower because it includes drivetrain loss. Crank HP is higher because it represents engine output before those losses.
For example, a vehicle may produce 500 HP at the engine but only 425 WHP at the wheels. In that case, the drivetrain loss is 75 horsepower, or 15% of the engine’s output.
This is why performance discussions can become confusing. One person might say their car makes 500 horsepower, meaning crank horsepower. Another person might say their car makes 500 horsepower, meaning wheel horsepower. Those are not the same. A 500 WHP car may actually be making 575 to 625 HP at the crank depending on drivetrain loss.
WHP to HP Formula
To convert wheel horsepower to crank horsepower, use this formula:
HP = WHP / (1 - Drivetrain Loss Percentage / 100)
Where:
HP = estimated crank horsepowerWHP = wheel horsepowerDrivetrain Loss Percentage = estimated percent of power lost through the drivetrain
For example, if the vehicle makes 350 WHP and the estimated drivetrain loss is 15%:
HP = 350 / (1 - 15 / 100)HP = 350 / 0.85HP = 411.76
The estimated crank horsepower is about 412 HP.
HP to WHP Formula
You can also reverse the formula to estimate wheel horsepower from crank horsepower:
WHP = HP × (1 - Drivetrain Loss Percentage / 100)
For example, if an engine is rated at 500 HP and the drivetrain loss is estimated at 15%:
WHP = 500 × (1 - 15 / 100)WHP = 500 × 0.85WHP = 425
The estimated wheel horsepower is 425 WHP.
Drivetrain Loss Formula
If you know both crank horsepower and wheel horsepower, you can calculate drivetrain loss:
Drivetrain Loss % = (1 - WHP / HP) × 100
For example, if a vehicle is rated at 450 HP and dynos at 380 WHP:
Drivetrain Loss % = (1 - 380 / 450) × 100Drivetrain Loss % = 15.56%
The estimated drivetrain loss is about 15.6%.
Common Drivetrain Loss Estimates
Drivetrain loss is not the same for every vehicle. It depends on drivetrain layout, transmission type, tire size, drivetrain design, dyno type, and testing conditions. However, the following ranges are commonly used for rough estimates:
| Drivetrain Type | Common Estimated Loss |
|---|---|
| Front-wheel drive | 10% to 15% |
| Rear-wheel drive | 12% to 18% |
| All-wheel drive | 18% to 25% |
| Manual transmission | Often lower |
| Automatic transmission | Often higher |
| Older drivetrain | Often higher |
| Modern efficient drivetrain | Often lower |
These are estimates, not fixed rules. A modern dual-clutch or efficient automatic may lose less power than an older automatic. A lightweight rear-wheel-drive car may have lower drivetrain loss than a heavy all-wheel-drive performance car. Tire size, wheel weight, gear selection, and dyno setup can also change the result.
Example: 300 WHP to HP
If a car makes 300 WHP and you assume a 15% drivetrain loss:
HP = 300 / 0.85HP = 352.94
So, 300 WHP is about 353 crank HP with a 15% loss.
If the same car has a 20% drivetrain loss:
HP = 300 / 0.80HP = 375
So, 300 WHP is about 375 crank HP with a 20% loss.
This shows why the drivetrain loss percentage matters so much. The same wheel horsepower number can produce different crank horsepower estimates depending on the assumed loss.
Example: 400 WHP to HP
If a car makes 400 WHP with a 15% drivetrain loss:
HP = 400 / 0.85HP = 470.59
So, 400 WHP is approximately 471 HP at the crank.
With an 18% drivetrain loss:
HP = 400 / 0.82HP = 487.80
With a 20% drivetrain loss:
HP = 400 / 0.80HP = 500
A 400 WHP car could reasonably be described as making around 470 to 500 crank horsepower depending on drivetrain layout and assumptions.
Example: 500 WHP to HP
If a vehicle makes 500 WHP and drivetrain loss is estimated at 15%:
HP = 500 / 0.85HP = 588.24
The estimated crank horsepower is about 588 HP.
If the drivetrain loss is 20%:
HP = 500 / 0.80HP = 625
The estimated crank horsepower is 625 HP.
This is why high-powered all-wheel-drive vehicles can have large differences between wheel horsepower and crank horsepower. The higher the output, the larger the horsepower difference becomes even if the percentage loss stays the same.
Why Wheel Horsepower Is Usually Lower Than Crank Horsepower
Wheel horsepower is lower because the drivetrain is not perfectly efficient. Power is lost as it moves through rotating components. Some energy becomes heat, friction, vibration, and rotational inertia.
The transmission is one of the biggest sources of drivetrain loss. Manual transmissions are often more efficient than traditional automatic transmissions, although modern automatics and dual-clutch transmissions can be very efficient. Torque converters, clutches, gears, shafts, bearings, and fluid drag can all affect how much power reaches the wheels.
The differential also absorbs power. So do axles, driveshafts, transfer cases, wheel bearings, and tires. All-wheel-drive vehicles typically have more drivetrain components than two-wheel-drive vehicles, which is why AWD drivetrain loss is often estimated higher.
Tires matter too. Large, heavy, sticky tires can absorb more power on a dyno than smaller, lighter tires. Wheel weight can also affect measured results because the dyno must accelerate the rotating mass.
Is Drivetrain Loss Really a Fixed Percentage?
Drivetrain loss is often discussed as a percentage, but in reality it is not perfectly fixed. Saying “this car has 15% drivetrain loss” is a useful shortcut, but the actual loss can vary with speed, gear, load, temperature, fluid viscosity, tire pressure, and dyno type.
Some drivetrain losses behave more like a fixed horsepower amount. Others scale with engine output or vehicle speed. That means a simple percentage is an estimate, not a laboratory measurement.
Still, the percentage method is useful because it gives a quick way to compare WHP and crank HP. For most calculator use cases, using a reasonable drivetrain-loss percentage is good enough to estimate the relationship between dyno numbers and advertised horsepower.
Dyno Type Can Affect WHP
Not all dynos read the same. A chassis dyno measures horsepower at the wheels, but different dyno designs and correction methods can produce different results.
Some dynos are known for reading higher or lower than others. Weather correction, tire pressure, gear selection, strap tension, fan setup, engine temperature, and smoothing settings can all affect the final number. Even the same car can produce different WHP numbers on different days.
This is why dyno results are best used as comparison tools. A before-and-after test on the same dyno, under similar conditions, is usually more meaningful than comparing one car’s dyno result to another car’s result from a different shop.
Why Manufacturers Advertise Crank HP
Vehicle manufacturers usually advertise crank horsepower because it represents engine output under controlled testing conditions. This makes it easier to compare engines independently of vehicle drivetrain layout.
For example, the same engine could be used in a rear-wheel-drive car, an all-wheel-drive car, or a truck. The engine’s crank horsepower may be the same, but the wheel horsepower could differ because each drivetrain has different losses.
Crank horsepower also avoids the variability of tire choice, dyno type, wheel weight, and drivetrain configuration. For official ratings, manufacturers need repeatable test standards. For enthusiasts and tuners, wheel horsepower is often more exciting because it shows what the car actually puts down.
Which Number Matters More?
Both numbers matter, but they answer different questions.
Crank horsepower is useful for comparing factory engine ratings. It is the number most manufacturers advertise. If you are comparing two stock vehicles from spec sheets, crank horsepower is usually the number you will see.
Wheel horsepower is useful for tuning, racing, and real-world performance discussion. It shows how much power reaches the pavement. If you want to know whether a modification actually improved performance, WHP is often the better number.
For acceleration, wheel horsepower is usually more directly relevant because it reflects power after drivetrain loss. However, weight, gearing, traction, torque curve, aerodynamics, and transmission behavior also matter. A car with less horsepower can still be faster if it is lighter, has better traction, or uses better gearing.
How to Use This WHP to HP Calculator
To use the calculator, enter the wheel horsepower and the estimated drivetrain loss percentage. The calculator will divide WHP by the remaining drivetrain efficiency to estimate crank horsepower.
For example:
Wheel Horsepower = 425 WHPDrivetrain Loss = 15%Estimated Crank HP = 500 HP
You can also use the calculator in reverse if it includes an HP to WHP mode. Enter crank horsepower and drivetrain loss to estimate wheel horsepower.
This is useful when comparing advertised horsepower to expected dyno results. If a car is rated at 600 HP and you assume 15% drivetrain loss, the expected wheel horsepower would be:
600 × 0.85 = 510 WHP
Choosing the Right Drivetrain Loss Percentage
The most important part of the calculation is choosing a realistic drivetrain loss percentage. For many rear-wheel-drive manual cars, 15% is a common estimate. For front-wheel-drive cars, 10% to 15% is often used. For all-wheel-drive cars, 18% to 25% is common.
A basic rule of thumb is:
| Vehicle Setup | Reasonable Starting Estimate |
|---|---|
| FWD manual | 10% to 13% |
| FWD automatic | 12% to 16% |
| RWD manual | 12% to 15% |
| RWD automatic | 15% to 18% |
| AWD manual | 18% to 22% |
| AWD automatic | 20% to 25% |
If you are unsure, 15% is a common default for many two-wheel-drive vehicles, while 20% is a common default for many all-wheel-drive vehicles.
WHP to HP Conversion Chart
Here are some common WHP to HP estimates using different drivetrain loss percentages:
| WHP | 10% Loss | 15% Loss | 20% Loss | 25% Loss |
|---|---|---|---|---|
| 200 | 222 HP | 235 HP | 250 HP | 267 HP |
| 300 | 333 HP | 353 HP | 375 HP | 400 HP |
| 400 | 444 HP | 471 HP | 500 HP | 533 HP |
| 500 | 556 HP | 588 HP | 625 HP | 667 HP |
| 600 | 667 HP | 706 HP | 750 HP | 800 HP |
| 700 | 778 HP | 824 HP | 875 HP | 933 HP |
| 800 | 889 HP | 941 HP | 1,000 HP | 1,067 HP |
The higher the drivetrain loss, the higher the estimated crank horsepower must be to produce the same wheel horsepower.
Why the Same WHP Can Mean Different Crank HP
A 450 WHP front-wheel-drive car and a 450 WHP all-wheel-drive car may not have the same crank horsepower. If the front-wheel-drive car has a 12% loss, the estimated crank horsepower is:
450 / 0.88 = 511 HP
If the all-wheel-drive car has a 22% loss, the estimated crank horsepower is:
450 / 0.78 = 577 HP
Both cars put 450 horsepower to the wheels, but the all-wheel-drive car may need more engine horsepower to do it because more power is lost through the drivetrain.
This does not automatically mean one car is faster than the other. All-wheel drive may provide better traction, especially from a launch. The front-wheel-drive car may have less drivetrain loss but struggle to put power down. Horsepower is only one part of the performance picture.
BHP vs WHP in Tuning
In tuning, WHP is often the preferred number because it is measured after modifications are installed. If you add a turbo upgrade, tune, intake, exhaust, or fuel system upgrade, the dyno shows how much power the car actually gained at the wheels.
BHP or crank HP is still useful when comparing the car to manufacturer ratings or estimating engine output. However, it is usually calculated from WHP unless the engine is removed and tested directly on an engine dyno.
For example, if a tuned car makes 520 WHP and you estimate 15% drivetrain loss, the crank horsepower is:
520 / 0.85 = 611.76 HP
So the car may be described as making roughly 612 HP at the crank. But the measured number is still 520 WHP.
Is Crank HP More Impressive Than WHP?
Crank horsepower numbers are usually larger, so they may sound more impressive. However, wheel horsepower is often the more honest number in enthusiast conversations because it is measured after drivetrain loss.
A car making 500 WHP is usually much more powerful than a car advertised at 500 crank HP. If both have a 15% drivetrain loss, the 500 crank HP car would make about 425 WHP, while the 500 WHP car would be closer to 588 crank HP.
When comparing builds, always check whether the number is WHP or crank HP. A simple label can completely change the meaning.
Limitations of WHP to HP Calculations
A WHP to HP calculator gives an estimate, not an exact measurement. The result depends heavily on the drivetrain-loss percentage entered. If that number is wrong, the estimated crank horsepower will also be wrong.
The calculator also cannot account for every variable that affects dyno results. Tire pressure, tire compound, wheel weight, dyno calibration, gear selection, air temperature, humidity, altitude, and correction factor can all influence the measured WHP.
For the most accurate crank horsepower number, the engine would need to be tested directly on an engine dyno. For most real-world use, however, estimating crank horsepower from WHP is a practical and common method.
Frequently Asked Questions
Is WHP the same as HP?
No. WHP is wheel horsepower, which is measured at the wheels. HP usually refers to crank horsepower or engine horsepower, which is measured or estimated before drivetrain loss. WHP is almost always lower than crank HP.
How do you convert WHP to HP?
To convert WHP to HP, divide wheel horsepower by drivetrain efficiency:
HP = WHP / (1 - drivetrain loss)
For example, with 400 WHP and 15% drivetrain loss:
400 / 0.85 = 470.6 HP
What is 400 WHP in crank HP?
400 WHP is about 471 crank HP with a 15% drivetrain loss. With a 20% drivetrain loss, 400 WHP is about 500 crank HP.
What is 500 WHP in crank HP?
500 WHP is about 588 crank HP with a 15% drivetrain loss. With a 20% drivetrain loss, 500 WHP is about 625 crank HP.
What drivetrain loss should I use?
For a rough estimate, use 10% to 15% for many front-wheel-drive cars, 12% to 18% for many rear-wheel-drive cars, and 18% to 25% for many all-wheel-drive cars. If you are unsure, 15% is a common default for two-wheel-drive vehicles and 20% is a common default for all-wheel-drive vehicles.
Is BHP the same as crank HP?
In most casual automotive discussions, BHP and crank HP are used to mean engine horsepower before drivetrain loss. Technically, brake horsepower is measured at the engine using a brake or engine dynamometer, while crank horsepower refers to power at the crankshaft. In practice, they are often treated as the same concept.
Why does AWD have more drivetrain loss?
All-wheel-drive vehicles usually have more drivetrain components, including a transfer case, extra driveshafts, additional axles, and more rotating parts. More components generally mean more friction and rotational loss, which can reduce the percentage of engine power that reaches the wheels.
Is WHP better than HP?
WHP is better for understanding real-world power at the wheels. HP or BHP is better for comparing factory engine ratings. Neither number is always “better”; they simply measure power at different points in the vehicle.
