How to use this calculator
- Enter ratings. Use GVWR and front/rear GAWR from the vehicle placard.
- Enter wheelbase. Measure from the front axle centerline to the rear axle centerline.
- Enter empty axle weights. Use unloaded front and rear axle scale weights when available.
- Place the loads. Measure each cargo, body or hitch load center of gravity from the front axle.
- Review margins. Check GVWR, front axle margin, rear axle margin and the remaining payload at the next load position.
How it works
The calculator models the front and rear axles as two static supports.
For a load at distance x from the front axle on a wheelbase
L, the load reactions are:
dR = W x x / L dF = W x (1 - x / L)
where dR is rear axle change and dF is front
axle change.
The calculated reactions are added to the measured empty axle weights, then compared with GVWR and GAWR. Use this after the truckload capacity calculator or freight density calculator when a load plan needs an axle-margin screen.
Worked example
Verified against the live calculator
With a 12 ft wheelbase, 3,600 lb empty front axle,
2,800 lb empty rear axle and the default three load groups,
gross vehicle weight is 9,800 lb. The front axle is about
4,129 lb, the rear axle is about 5,671 lb,
and the GVWR margin controls the next load at about 2,200 lb.
Frequently asked questions
How do you calculate truck axle load from cargo position?
Treat the front and rear axles as two supports. A load W at distance x from the front axle changes rear axle load by W x x/L and front axle load by W x (1 - x/L), where L is wheelbase.
Why does a rear overhang load add more to the rear axle than its own weight?
When a load center is behind the rear axle, x is greater than the wheelbase. The rear axle carries more than W and the front axle reaction becomes negative, so the load unloads the front axle.
Should I use curb weight or scale weights?
Use measured empty front and rear axle scale weights when possible. Published curb weight usually misses upfits, tools, fuel level, accessories and fleet equipment.
Is this a legal truck weight calculator?
No. It is a static planning screen for two-axle support reactions. Real dispatch decisions need certified scale weights, tire ratings, manufacturer ratings, bridge-law and axle-group rules, securement and route limits.
Method & assumptions
- The model is static and planar, with the vehicle reduced to one front axle support and one rear axle support.
- Load positions are center-of-gravity estimates measured from the front axle centerline.
- It does not model tandem axle equalization, bridge formula limits, suspension compliance, dynamic braking or cornering transfer, securement, tire sidewall ratings or road-grade effects.
- Final dispatch, towing and road-use decisions still need certified scale weights, manufacturer placards, tire ratings, hitch ratings, bridge-law checks, axle-group rules and local regulations.