Roof Rack & Box Payload Budget Calculator

Compare dynamic roof, rack and box ratings in kg. Subtract the correct equipment weights, review cargo headroom and save an installer worksheet.

Roof Rack & Box Payload Worksheet
Source review: 2026-10-03; kg; 2026
Started from fictional example: false
Status: pending
Load mode: dynamic
Vehicle dynamic roof limit V: Unconfirmed
Complete rack weight R: Unconfirmed
Empty box weight B: Unconfirmed
Rack / crossbar limit X: Unconfirmed
Roof box limit Y: Unconfirmed
Rack rating basis: Unconfirmed
Box rating basis: Unconfirmed
dynamicConfirmed: false
ratingsConfirmed: false
cargoWeighed: false
Vehicle reference: 
Rack reference: 
Box reference: 
1. : Unconfirmed × 1
Cargo total: Unconfirmed
Total roof weight: Unconfirmed
Input-based common cargo ceiling: Unconfirmed
Ratings-confirmed payload budget: Unconfirmed
Weighing-confirmed additional budget: Unconfirmed
Required reduction: Unconfirmed
Empty-equipment excess: Unconfirmed
Limiting constraints: Unconfirmed
Missing confirmations: vehicleLimit, rackWeight, boxWeight, rackLimit, boxLimit, rackBasis, boxBasis, dynamicConfirmed, ratingsConfirmed, cargoWeighed, cargo.0.weight
Invalid fields: 
vehicle: limit/actual/cargo ceiling/margin/excess/empty-equipment excess = Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed
rack: limit/actual/cargo ceiling/margin/excess/empty-equipment excess = Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed
box: limit/actual/cargo ceiling/margin/excess/empty-equipment excess = Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed / Unconfirmed
Hypothetical comparison: unchanged ratings and bases; no prediction of replacement-product performance.
current: R=Unconfirmed, B=Unconfirmed, Y=Unconfirmed; C=Unconfirmed
lighter-rack: R=Unconfirmed, B=Unconfirmed, Y=Unconfirmed; C=Unconfirmed
lighter-box: R=Unconfirmed, B=Unconfirmed, Y=Unconfirmed; C=Unconfirmed
higher-box-limit: R=Unconfirmed, B=Unconfirmed, Y=Unconfirmed; C=Unconfirmed
Vehicle Cv=V−R−B; rack Cr=X / X−B / X−R−B; box Cb=Y / Y−B; C=min(Cv,Cr,Cb).
This compares ratings and listed cargo only. Confirm fitment, vehicle gross/axle mass, securing, clearance and local rules separately. It is not a safety, installation or static sleeping-load approval.
Korean Road Traffic Act Article 39 MST281875 effective 2026-07-01; Decree Article 22 MST290387 effective 2026-10-02. Korean-road context only; no uplift to product kg ratings.
https://www.thule.com/en-us/articles/tips/how-to-pack-safely-with-a-roof-box
https://www.thule.com/-/s/approved/std.lang.all/37/97/463797.pdf
https://www.law.go.kr/%EB%B2%95%EB%A0%B9/%EB%8F%84%EB%A1%9C%EA%B5%90%ED%86%B5%EB%B2%95/%EC%A0%9C39%EC%A1%B0
https://www.law.go.kr/%EB%B2%95%EB%A0%B9/%EB%8F%84%EB%A1%9C%EA%B5%90%ED%86%B5%EB%B2%95%EC%8B%9C%ED%96%89%EB%A0%B9/%EC%A0%9C22%EC%A1%B0

No universal vehicle rating is assumed. Check dynamic ratings and what each rating includes. A mass comparison alone cannot establish installation or road safety.

Sources reviewed 2026-10-03 · kg · Korean-road context: Act Article 39 2026-07-01 / Decree Article 22 2026-10-02

1. Vehicle and equipment ratings

Load condition

Vehicle dynamic roof limit V (kg)

In-motion limit including the rack, box and all cargo.

Complete rack weight R (kg)

Include bars, feet and rack adapters. Count each fitting once.

Empty box weight B (kg)

Include box fittings that are not already counted in R.

Rack / crossbar limit X (kg)

Use the lowest applicable assembly rating; select its weight basis.

Roof box limit Y (kg)

Check whether its manual rates cargo alone or box plus cargo.

Weight included in rack rating X

Weight included in box rating Y

Select the exact documented basis. Do not double a rating for two bars or count one fitting in both empty weights.

2. Cargo list including packaging

Item 1

Weight per item (kg)

Include its bag and packaging.

Quantity

Whole number from 1 to 100.

Current cargo total: Unconfirmed

3. References and confirmations

Vehicle, model year, roof option and manual

Rack, feet, kit and rating definition

Box model, rating definition and weighing date

The vehicle rating is dynamic and includes rack, box and cargo.I checked model year, roof option, assembly ratings, empty weights and weight bases against the manuals.I weighed the full cargo list, including bags, packaging and liners.

Payload budgets and limiting constraints

Confirm ratings, weight bases and measurements

Ratings-confirmed payload budget

Unconfirmed

Weighing-confirmed extra cargo

Unconfirmed

Input-based required reduction

Unconfirmed

Input-based common cargo ceiling (assumption): Unconfirmed

Rack + box + cargo roof weight: Unconfirmed

Limiting constraints (entered values): Unconfirmed

Empty-equipment excess: Unconfirmed

Unconfirmed items (11)

Vehicle dynamic roof limit V
Complete rack weight R
Empty box weight B
Rack / crossbar limit X
Roof box limit Y
Rack rating weight basis
Box rating weight basis
The vehicle rating is dynamic and includes rack, box and cargo.
I checked model year, roof option, assembly ratings, empty weights and weight bases against the manuals.
I weighed the full cargo list, including bags, packaging and liners.
Cargo 1: weight, quantity or name

Independent component ratings, actual weights, cargo ceilings, margins and excesses
Constraint	Original rating	Actual on this basis	Cargo ceiling	Margin with cargo	Excess
Vehicle roof	Unconfirmed	Unconfirmed	Unconfirmed	Unconfirmed	Unconfirmed
Rack / crossbars	Unconfirmed	Unconfirmed	Unconfirmed	Unconfirmed	Unconfirmed
Roof box	Unconfirmed	Unconfirmed	Unconfirmed	Unconfirmed	Unconfirmed

Unconfirmed does not mean 0 kg. A negative ceiling means the empty assembly is already over its rating. Positive headroom does not confirm fitment, securing, vehicle gross/axle mass or road legality.

Equipment comparison assuming unchanged ratings

Only the specified weight or box rating changes. Real replacements require a new rating and fitment review. Reduced empty weights never fall below 0 kg.

Current inputs

Input-based cargo ceiling: Unconfirmed

R Unconfirmed · B Unconfirmed · Y Unconfirmed

Rack up to 1 kg lighter

Input-based cargo ceiling: Unconfirmed

R Unconfirmed · B Unconfirmed · Y Unconfirmed

Box up to 5 kg lighter

Input-based cargo ceiling: Unconfirmed

R Unconfirmed · B Unconfirmed · Y Unconfirmed

Box rating +5 kg

Input-based cargo ceiling: Unconfirmed

R Unconfirmed · B Unconfirmed · Y Unconfirmed

Related calculators

Why roof payload needs three separate checks

A large roof box can provide more space without providing more weight capacity.
Cargo is supported by the box, rack assembly and vehicle roof, each with its own rating and weight definition.
This calculator converts all three ratings into cargo-only ceilings and takes the smallest one.
Use it before buying a box or packing for a family trip to identify the limiting component and the weight of cargo that remains in your budget.

Your next action

Record the exact vehicle model, year and roof option, the rack feet and fitting kit, and the box model.
Save the worksheet with manual references and a weighed cargo list, then ask the installer or manufacturer about any unconfirmed rating.
A positive margin still requires separate fitment, fastening and operating-condition checks.

What the calculator reports

Payload and extra-cargo budgets

The payload budget is the ceiling before loading cargo.
The additional budget subtracts your existing cargo and requires confirmation that the complete list has been weighed.
Negative input ceilings are retained as evidence that the empty assembly already exceeds a rating.

Constraints and overloads

Compare each original rating, actual mass on that rating’s basis, cargo ceiling, margin and excess.
A star identifies the limiting component, including ties.
Known overloads remain visible even when other information is missing.

Hypothetical equipment comparisons, a missing-data checklist, TXT export and a printable worksheet help you take the same assumptions to an installer.
These comparisons do not recommend or predict the performance of replacement products.

Vehicle ratings and empty equipment weights

V: vehicle dynamic roof rating

Use the in-motion roof rating for your actual model year and roof option.
V must include rack, box and cargo together.
Do not substitute another vehicle’s rating or a parked-vehicle rating.
If the dynamic basis or included mass is unclear, leave its confirmation unchecked and consult the manufacturer.

R and B: empty assembly weights

R includes the complete rack: bars, feet and rack adapters.
B includes the empty box and its dedicated fittings, excluding anything already counted in R.
Count a fitting once, distinguish shipping packaging from installed hardware, and include both bars in the rack weight.
Record removable bags, liners and packing materials in the cargo list.

X and Y: independent product ratings

X is the lowest documented rating applicable to the installed rack, feet and fitting-kit combination.
Y is the rating for the exact box model.
Two bars do not automatically double the assembly rating, and a stronger rack does not increase the vehicle roof rating.
All mass inputs use kg, up to two decimal places; the 0–10,000 kg input range is a software guard, not an approved load range.

Confirm what each rating includes

Subtracting every empty weight from every rating can double-count deductions; subtracting none can overstate headroom.
Choose the documented definition, rather than the definition that gives the largest result.

Rack rating for cargo only: use X.
Rack rating for box plus cargo: use X − B.
Rack rating for rack, box and cargo: use X − R − B.
Box rating for cargo only: use Y; box-inclusive rating: use Y − B.

Unconfirmed means unconfirmed

An unknown rack or box weight basis withholds that cargo ceiling and the common ceiling.
Blank values are not zero or unlimited capacity.
An explicit 0 kg means an actual zero mass or no permitted capacity.
For a definition that does not match these choices, ask the manufacturer how to normalize it before calculating.

Payload and overload formulas

Normalize the three constraints

Cv = V − R − B
Cr = X / X − B / X − R − B
Cb = Y / Y − B
C = min(Cv, Cr, Cb)
P = Σ(weight per item × quantity)

Apply just the Cr and Cb formula matching the confirmed basis.
C exists only when all three ceilings are known.
The ratings-confirmed payload budget is max(0, C); C below zero indicates an empty-equipment problem.

Include existing cargo

Total roof weight is R + B + P.
Each constraint’s margin is its cargo ceiling minus P.
After ratings, dynamic basis and weighing are confirmed, additional headroom is max(0, C − P).
An empty list or any unweighed item withholds P.

Precision and required reduction

Calculations use integer hundredths of a kg to avoid boundary drift.
Required reduction is max(0, P − C), and empty-equipment excess is max(0, −C).
When C is negative, removing every cargo item cannot fix the empty assembly itself.
No universal safety factor is invented.

Step-by-step use before a journey

Prepare manuals and plates for the actual vehicle, roof option, rack kit and box.
Select dynamic in-motion loading; enter the vehicle total roof limit and complete empty equipment weights.
Enter rack and box limits and select their documented weight bases; keep unclear data unconfirmed.
Weigh each item with bags and packaging, enter quantity from 1 to 100, and review up to 20 item types.
Check only the confirmations you have completed; loading the fictional example checks none.
Review overloads, limiting components and missing data, then save or print the installer worksheet.

If you move cargo inside the vehicle, separately check vehicle gross mass and interior loading.
More roof headroom does not create additional gross-vehicle capacity.
References can record manual pages, model versions and weighing dates; they are not automatically verified by this tool.

Worked example: 75 kg roof and 45 kg cargo box

This is fictional arithmetic, not a specification for any vehicle or product.
V=75 kg, R=5 kg, B=20 kg, X=75 kg on a box-plus-cargo basis, and Y=45 kg on a cargo-only basis.
Two 12 kg bags and two 8 kg bedding items make P=40 kg.

Independent cargo ceilings and margins with 40 kg of cargo
Constraint	Conversion	Ceiling kg	Margin kg
Vehicle	75 − 5 − 20	50	10
Rack	75 − 20	55	15
Box ★	45	45	5

The common cargo ceiling is 45 kg and total roof mass is 65 kg.
After all confirmations, additional headroom is 5 kg, limited by the box.
At 45 kg cargo you reach the limit; at 45.01 kg you exceed it by 0.01 kg.
If X instead equals 50 kg including rack, box and cargo, its ceiling is 25 kg and the current cargo exceeds it by 15 kg.

Read status and missing-data messages correctly

Pending and exceeded

Missing numbers, weight bases or confirmations produce a pending review.
An overload already visible in a known constraint takes priority, with the missing-data list retained.
Passing a known constraint never implies passing an unknown one.
An input-based ceiling shown with unchecked confirmations remains an assumption, not a confirmed budget.

At limit and within ratings

These states require complete data and all confirmations.
At limit means no extra cargo margin.
Within ratings describes the entered mass checks only; it does not assess wind, bumps, braking, center of gravity, fastening condition or road legality.

Empty equipment already exceeds a rating

For V=20 kg, R=5 kg and B=20 kg, Cv=−5 kg.
The empty rack and box exceed the vehicle rating by 5 kg before cargo is added.
Review the assembly and source values rather than treating cargo removal as a complete solution.

Compare equipment assumptions before buying

In the worked example, a rack 1 kg lighter still gives C=45 kg; a box 5 kg lighter also gives C=45 kg.
The box cargo limit remains the bottleneck even though vehicle and rack margins improve.
Raising only the box cargo rating by 5 kg gives C=50 kg, with vehicle and box tied.
Use this to investigate which constraint actually needs attention.

Comparison assumptions

All other ratings and weight bases remain unchanged in each scenario.
Real replacement products may change those ratings and fitment, so enter their actual documentation separately.
Weight reductions stop at 0 kg; the scenario card shows the resulting R, B and Y values.
Unknown information continues to withhold a common ceiling, and no scenario automatically confirms replacement equipment.

Weighing, securing and scope limits

Liters describe box volume, not cargo mass; this calculator does not convert liters into kg.
Parked rooftop-tent sleeping loads are static and outside scope; dynamic limits are not multiplied into a person capacity.
Multiple roof carriers, bicycles or parallel accessories require a separate load-path and component-rating review.
Check weight distribution, cargo restraint, box locks, rack spacing and hatch clearance against the installation instructions.
Measure overall height and garage clearance separately; the tool does not predict speed, fuel use or structural safety.

Verify which installed fittings are included in published empty weights.
Reweigh the full list after packing changes.
Keep estimates and measured values distinguishable in your references, and separately check vehicle gross and axle ratings.

Frequently asked questions

Can a higher-rated box override my roof rating?

No.
The smallest normalized vehicle, rack or box ceiling controls the budget.
A stronger rack or box does not increase vehicle roof capacity.

Must I always subtract rack weight from the rack rating?

No.
Select the manufacturer’s documented cargo-only, box-plus-cargo or complete-assembly basis.
Leave an unclear definition unconfirmed rather than guessing.

How do blanks differ from 0 kg?

Blank means unconfirmed; zero is a stated zero mass or no permitted capacity.
A single unknown item weight withholds the whole cargo total.

Can I use the static roof rating?

No.
Static and unknown load modes withhold this in-motion calculation.
Rooftop-tent occupant loads and ladder support require a separate product review.

Does the example confirm the checklist?

No.
Its values are fictional and all confirmations remain unchecked.
Replace them with actual documentation and measured cargo before checking the relevant boxes.

Why is there an overload with no cargo?

The empty rack and box can already exceed a component or vehicle rating.
Review the negative cargo ceiling and empty-equipment excess, then check the assembly and source inputs.

Does within ratings mean road approval?

No.
It compares entered mass constraints only.
Fitment, fastenings, gross/axle mass, clearance, local permissions and securing duties remain separate checks.

Where do my entries go?

The form does not submit your entered ratings and cargo to a separate server.
TXT export creates a local browser file containing inputs, bases, confirmations, results and sources.
You arrange any installer or manufacturer consultation yourself.

Official sources and your review worksheet

Sources reviewed 2026-10-03; context year 2026

Thule official packing guide: source for dynamic/static distinction and separate vehicle, rack and box limits.
Thule FORCE assembly instructions 5015943_05: model-specific reference, not a universal rating.
Korean Road Traffic Act Article 39: official API current ID001638/MST281875, effective 2026-07-01; domestic loading and cargo-securing context.
Korean Road Traffic Act Enforcement Decree Article 22: current ID003395/MST290387, effective 2026-10-02; its 110% provision for freight vehicles is not an uplift to passenger-car roof or product ratings.

The product calculation is global; the legal notes describe Korean roads and do not decide compliance elsewhere.
Product-specific kg ratings come from applicable manuals, not a universal legal value.
Recheck law effective dates, model years, manual revisions and included-weight definitions when maintaining the tool.

Use the plates, manuals and weighed list together

Complete missing inputs, save the worksheet and confirm the component ceilings with your installer.
Before departure, separately check fastening and overall height.
For other travel equipment, see the caravan towing weight calculator or camper and caravan cost calculator.