Shipping cost by weight calculator
Price a parcel from its weight in two clear steps: 3.5 kg at 1.80 per kilogram is a 6.30 weight charge, and a 4.25 base charge brings the shipping cost to 10.55. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Actual weight
- 3.5
- Base charge
- 4.25
- Rate per unit
- 1.8
- Weight unit
- Kg
- Weight charge
- 6.3
- Shipping cost
- 10.55
The shipping cost by weight calculator combines a carrier's fixed base charge with a rate applied to the parcel's actual weight. Enter the weight, choose kilograms or pounds, and supply the matching rate per unit. The result separates the weight-based charge from the final shipping cost, making the calculation easy to verify and reuse in a checkout, quote, spreadsheet replacement, support workflow, or fulfillment process. It performs direct arithmetic without carrier lookups, dimensional-weight rules, zones, taxes, or hidden adjustments.
Enter a consistent weight and rate
The calculator does not convert between measurement systems because an automatic conversion could conceal a mismatched tariff. If a parcel weighs 3.5 kilograms and the rate is 1.80 per kilogram, enter 3.5, 1.80, and kg together. Use non-negative finite numbers and keep all monetary inputs in the same currency.
Zero is accepted for any numeric field, which supports free base service, a temporarily waived weight rate, or a zero-weight test case. The capability deliberately receives numbers rather than formatted currency strings, so remove symbols and grouping separators before calling it. Your application remains responsible for displaying the returned amounts with the correct currency symbol, locale, and number of decimal places.
This explicit contract makes input errors visible instead of silently mixing pounds with a kilogram rate or treating formatted text as money.
Understand the calculation and returned breakdown
The calculation has two steps. The response also repeats the validated weight, unit, base charge, and rate, so a quote can retain the assumptions behind its total. For a 3.5-kilogram parcel, a base charge of 4.25, and a rate of 1.80 per kilogram, the weight component is 6.30 and the total is 10.55.
Apply that business rule after receiving the result. Keeping mathematical normalization separate from currency presentation prevents the calculator from imposing one market's billing convention on every caller.
Know which shipping rules belong upstream
Use this capability when the tariff is genuinely a fixed charge plus a linear price for actual weight. Before calling it, determine the parcel weight according to your operational process and select the correct rate from your own carrier agreement, service level, destination zone, or product policy. The calculator does not fetch live carrier prices, compare services, calculate dimensional weight, choose the greater of actual and dimensional weight, round a parcel up to a billing increment, or add fuel surcharges, insurance, handling fees, taxes, duties, and remote-area charges.
Those decisions belong upstream because they vary by contract and shipment. If a carrier bills every started kilogram, round the actual weight upward before sending it; if it uses billable weight, calculate that value first and pass it only when it represents the weight you intend to price. Preserve the returned breakdown with the source tariff for auditing, and format the amount in your checkout currency afterward.
Identical inputs always produce identical output, so the solver works consistently in browser estimates, server-side order checks, batch quote preparation, automated tests, and customer-support tools.
What you can do with it
Storefront shipping estimates
Calculate a transparent delivery estimate when a store uses a fixed charge plus a linear actual-weight rate.
Fulfillment quote checks
Verify the weight component and final total before a shipment is handed to a carrier or warehouse.
Customer support explanations
Give agents a repeatable breakdown showing how parcel weight contributes to a quoted shipping cost.
FAQ
Does it convert kilograms to pounds?
No. Choose kg or lb and provide both the parcel weight and rate in that same unit.
Does it calculate dimensional or billable weight?
No. It prices the weight you supply. Calculate any dimensional, rounded, or billable weight separately when your carrier requires it.
Are surcharges, taxes, and insurance included?
No. The result contains only the supplied base charge and linear weight charge. Add other contract-specific amounts in your own workflow.
How is shipping cost by weight calculated?
Multiply the parcel weight by the rate per unit to get the weight charge, then add the fixed base charge. A 3.5 kg parcel at 1.80 per kilogram gives 6.30, plus a 4.25 base, for 10.55.
What if my carrier bills every started kilogram?
Round the weight up to the next whole unit yourself before entering it. The calculator uses the weight exactly as given, and if your carrier bills on billable weight, work that figure out first and enter it instead.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/ecom/shipping-cost-by-weight \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"actual_weight":3.5,"base_charge":4.25,"rate_per_unit":1.8,"weight_unit":"kg"}'const res = await fetch("https://api.kit.forhosting.com/ecom/shipping-cost-by-weight", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"actual_weight": 3.5,
"base_charge": 4.25,
"rate_per_unit": 1.8,
"weight_unit": "kg"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/ecom/shipping-cost-by-weight",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"actual_weight": 3.5,
"base_charge": 4.25,
"rate_per_unit": 1.8,
"weight_unit": "kg"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/ecom/shipping-cost-by-weight", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"actual_weight":3.5,"base_charge":4.25,"rate_per_unit":1.8,"weight_unit":"kg"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"actual_weight":3.5,"base_charge":4.25,"rate_per_unit":1.8,"weight_unit":"kg"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/ecom/shipping-cost-by-weight", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"actual_weight": 3.5,
"base_charge": 4.25,
"rate_per_unit": 1.8,
"weight_unit": "kg"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "ecom.shipping_cost_by_weight",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Enter a consistent weight and rate
Start with the parcel's actual_weight, the fixed base_charge, and the carrier's rate_per_unit. Then set weight_unit to kg when both the parcel weight and rate are expressed per kilogram, or lb when both are expressed per pound.
Understand the calculation and returned breakdown
First, actual_weight is multiplied by rate_per_unit to produce weight_charge. Second, base_charge is added to weight_charge to produce shipping_cost. The same formula applies to pounds when weight_unit is lb; no conversion occurs because the supplied rate already corresponds to the selected unit.
Know which shipping rules belong upstream
Each API calculation costs $0.002, while the browser calculator uses the same pure logic.
Technical questions
What formula does the calculator use?
It calculates weight_charge as actual_weight multiplied by rate_per_unit, then calculates shipping_cost as base_charge plus weight_charge.
How much does an API calculation cost?
Each API request costs $0.002. The browser calculator runs the same deterministic solver free of charge.