Litres consumed per 100 kilometres; lower is better. Standard metric efficiency unit.

Energy lost deforming tires as they roll. Low-pressure or wide tires raise it.

Automotive Calculators

Radiator Capacity Calculator

2026-09-27 6 min

Compute coolant capacity of a radiator from core length, height, thickness and tube volume share.

Radiator Capacity: 2.48 gal; Coolant held by the radiator
Capacity (metric): 9.37 L; Liters of coolant

Calculator

Core Length(in) Help

Finned width

Core Height(in) Help

Finned height

Core Thickness(in) Help

Tank to tank of core

Tube Volume Share(%) Help

Share of core that holds coolant

Results update live as you type

Live statistics

Radiator Capacity

2.48 gal

Coolant held by the radiator

Capacity (metric)

9.37 L

Liters of coolant

Results

Optimal

Radiator Capacity

2.48gal

Coolant held by the radiator

Capacity (metric)

9.37L

Liters of coolant

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

Visualizations

Results overview

2.5Radiator Capacity

9.4Capacity

Radiator Capacity vs. Core Length

Radiator Capacity

2.5gal

Formula

Core box volume times the share occupied by coolant tubes (fins and air make up the rest), converted from cubic inches to gallons.

gal = L x H x T x tube% / 231

Alternative Form

Liters = gallons x 3.78541 (231 cu in per US gallon)

Variables

Symbol	Name	Unit	Description
L,H,T	Core dimensions	in	Finned length, height, thickness
tube%	Tube share	%	Typically 50-60% for tube-and-fin cores

Explanation

A radiator is mostly air passages; only the tubes hold coolant. Multiplying box volume by tube share gives the fill volume used for mixing coolant.

Step-by-Step Calculation

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

Step 1

Record the inputs.

Core Length:26 in

Core Height:16 in

Core Thickness:2.5 in

Tube Volume Share:55 %

Result: 4 inputs ready

Step 2

Apply the formula.

gal = L x H x T x tube% / 231

Result: Primary result = 2.48 gal

Step 3

Read every derived output.

Radiator Capacity:2.48 gal

Capacity (metric):9.37 L

Result: Radiator Capacity = 2.48 gal

Final Answer

2.48

Worked Examples

See how the calculator works with different scenarios.

Scenario

Typical performance replacement radiator.

Inputs

Core:26 x 16 x 2.5 in

Tubes:55%

Calculation

26 x 16 x 2.5 x 0.55 / 231 = 2.48 gal

Result

2.48 gal (9.4 L) in the radiator alone.

Interpretation

Add engine block, heater core and hoses for total system capacity.

Understanding Your Result

Your Result: Radiator Capacity: 2.48 gal

What This Means

How many gallons of coolant the radiator itself holds — the starting point for mixing the system fill.

Why It Matters

Coolant is mixed by concentration of the total system; knowing the radiator share prevents under-buying antifreeze.

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

Radiator capacity is one slice of total cooling-system volume alongside the block, heater core and hoses.

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)

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

Practical Tips

•Use 55% tube share unless the manufacturer states otherwise
•Add ~0.5 gal for tanks on downflow radiators
•Record the number for your coolant-mix math

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.

How much coolant does a radiator hold?

Most car radiators hold 1.5-3 gallons by themselves; the full system (block, heater, hoses) is typically 3-5 gallons.

What is tube volume share?

The fraction of core volume inside coolant tubes versus fins/air. Use ~55% for tube-and-fin, ~65% for bar-and-plate.

Related Calculators

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Related Guides

Deepen your understanding with these educational resources.

Automotive Guides

Build planning, measurement protocol and validation how-tos

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.

EPA — FuelEconomy.gov DOE — Fuel-Efficient Driving Tips NHTSA — Driving Safety & Efficiency SAE International — Fuel Economy Standards Consumer Reports — MPG Truth IRS — Standard Mileage Rates

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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Last Updated:

2026-09-27

Version:

2.0.0

References:

License:

Free to use for educational and professional purposes.