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Automotive Calculators

Turning Circle Calculator

2026-09-27 6 min

Curb-to-curb and wall-to-wall turning diameters from turn radius and vehicle width.

Curb to Curb
40.0 ft
Tire-path diameter
Wall to Wall
46.5 ft
Including body swing

Calculator

Turning Radius(ft) Help
ft

To outer tire

Vehicle Width(ft) Help
ft

Mirror to mirror

Results update live as you type

Live statistics

Curb to Curb

40.0 ft

Tire-path diameter

Wall to Wall

46.5 ft

Including body swing

Results

Optimal

Curb to Curb

40.0ft

Tire-path diameter

Wall to Wall

46.5ft

Including body swing

Planning estimate from standard automotive formulas. Validate with dyno, timeslip or datalog data when precision matters.

Visualizations

Results overview

40Curb to Curb
46.5Wall to Wall

Wall to Wall vs. Turning Radius

Wall to Wall

46.5ft
080

Formula

Doubles the radius to a diameter, then adds body width for the swept wall clearance.

Curb-to-curb = 2 x radius; wall-to-wall adds vehicle width

Alternative Form

Wall-to-wall is the real garage/alley number (body overhang swings wide)

Variables

SymbolNameUnitDescription
WWidthftMirrors included

Explanation

Spec sheets quote curb-to-curb (tires); your garage cares about wall-to-wall (bumpers and mirrors).

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Record the inputs.

Turning Radius:20 ft
Vehicle Width:6.5 ft
Result: 2 inputs ready
Step 2

Apply the formula.

Curb-to-curb = 2 x radius; wall-to-wall adds vehicle width
Result: Primary result = 46.5 ft
Step 3

Read every derived output.

Curb to Curb:40.0 ft
Wall to Wall:46.5 ft
Result: Wall to Wall = 46.5 ft
Final Answer
40.0

Worked Examples

See how the calculator works with different scenarios.

Scenario

Garage U-turn check.

Inputs

Radius:20 ft
Width:6.5 ft

Calculation

C2C = 40 ft; W2W = 46.5 ft

Result

40-ft tires, 46.5-ft walls.

Interpretation

Needs a 47-ft clear width — most residential streets fail; 3-point it.

Understanding Your Result

Your Result: Curb to Curb: 40.0 ft

What This Means

Street width a U-turn really consumes.

Why It Matters

Separates optimistic spec numbers from body-swing reality.

Professional Interpretation

Treat the primary result as a planning estimate, then validate on a dyno, at the track, or with logged sensor data. If measured numbers disagree by more than ~10%, re-check inputs (units are the usual culprit) before changing parts.

Recommendations

  • •Double-check units on every input before trusting the result
  • •Compare against the worked example below to sanity-check magnitude
  • •Validate with measured data (dyno, timeslip, datalog) when it matters

Learn — fuel economy, deeply

Turning circles come in tire and body flavors.

1 · Where the gallon goes (energy path)

Engine heat

60–70% lost

Coolant + exhaust carry most energy away. Hybrids recover some via Atkinson cycle + regen.

Driveline

5–15% lost

Transmission, differential, accessories. CVTs and 8–10 speed autos lose less.

Aero drag

∝ v²

Doubles from 55→78 mph. Roof boxes hurt more than trunks.

Rolling + brakes

10–20%

Tires, weight, stops. Regen braking (hybrid/EV) reclaims city braking energy.

4 · Measure like a pro (the 3-tank protocol)

  1. Fill to first click at the same pump, record the odometer (Tank 0).
  2. Drive normally for 2–3 tanks; always refill to first click at the same pump.
  3. MPG = total miles ÷ total gallons across all tanks — averaging kills pump-click noise.
  4. Cross-check with the trip computer; a persistent >10% gap means the computer needs calibration — or the car needs service.
  5. Log with an OBD-II dongle for per-trip MPG if you want to isolate commute vs. highway behavior.

Practical Tips

  • •Use wall-to-wall for structures
  • •Fold mirrors where possible
  • •Trailers roughly double the need

Common Mistakes

Mixing units (inches with mm, psi with kPa)
Convert every input to the unit shown on its field before calculating.
Trusting a single output blindly
Cross-check with the worked example and, when it matters, a dyno or datalog.

Assumptions

This calculator makes the following assumptions to provide estimates:

Steady-state model: Formulas assume stabilized conditions; transients, heat soak and traction limits are excluded.
Standard factors: Empirical constants (BSFC, VE, drivetrain loss) use typical values — your combination may differ.

Limitations

Be aware of these limitations when using this calculator:

Estimate, not measurement: Predictions carry real-world scatter of roughly ±5–15% depending on the model.
No transient effects: Shift time, wheelspin, spool lag and heat soak are not modeled here.

Frequently Asked Questions

Answers to common questions about this calculator.

Curb-to-curb vs wall-to-wall?
Curb = tire paths; wall adds body/mirror swing (~vehicle width). Use wall for garages and alleys.
How wide for a U-turn?
Wall-to-wall plus 2-3 ft comfort — typically 40-55 ft for trucks and SUVs.

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Related Guides

Deepen your understanding with these educational resources.

Glossary

Technical terms used in mortgage calculations explained in plain language.

MPG
Miles per gallon. Distance travelled per gallon of fuel; higher is better. US gallon = 3.785 L.
L/100 km
Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.
MPGe
Miles per gallon-equivalent. EV metric: miles travelled on 33.7 kWh (energy of 1 gal of gasoline).
CAFE
Corporate Average Fuel Economy — US fleet-average efficiency standard enforced by NHTSA.
Rolling resistance
Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.
Aerodynamic drag
Air resistance growing with the square of speed — why highway MPG falls fast above 60 mph.
Hypermiling
Driving techniques (coasting, steady speed, anticipation) that maximise real-world MPG.
OBD-II
On-board diagnostics port. Scanners and dongles read live MPG, fuel trim and fault codes.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

EPA Fuel Economy Testing (40 CFR Part 600)CAFE — Corporate Average Fuel Economy Standards (NHTSA)WLTP — Worldwide Harmonised Light Vehicle Test ProcedureSAE J1321 / J1711 — Fuel consumption test proceduresISO 2575 — Road vehicles symbols & efficiency markings

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