Why one inch can nearly double your courier charge: reading a rate card

Take two cartons that differ by one inch in height. Put the same light product in each.

On some rate cards, the taller carton costs nearly twice as much to ship.

It looks like a billing mistake... it is not.

Here is the short answer. Courier charges rise in steps called slabs, not gram by gram. The courier takes the higher of the actual weight and the volumetric weight, rounds it UP to the top of its slab, and charges the whole slab. A parcel sitting just under a slab line can cross it with one inch or a few grams, and then you pay one full additional slab.

On small parcels, that additional slab can cost almost as much as the first one.

We make tapes, films and paper packaging at Jagannath Polymers in Jaipur, and our ecommerce wing sends parcels through couriers as well. So we read these cards from both sides of the counter.

I cannot tell you your rates. I do not see your contract, and rates change faster than any guide can follow. What I can show you is how a rate card is built, where its cliffs are, and how to find them on your own card before a carton change finds them for you.

The volumetric formula, the divisors and the right way to measure a parcel are in our separate guide on volumetric weight. Here we stay with the rate card itself.

How is a courier rate card laid out?

Most rate cards we have worked with have the same four parts, whatever the courier.

1. Rows are weight slabs. The first row is the first slab, often up to 500 g. Then come the rows for each additional slab.
2. Columns are zones. The zone depends on where the parcel is picked up and where it is delivered.
3. Each service (air, express, surface) usually has its own table, and some cards also split by size.
4. The notes hold the rules: the divisor, the rounding, the size limits and the surcharges.

Let us look at two published examples. I checked both on 22 October 2026.

India Post's Speed Post Parcel (Domestic) page shows rates effective from 1 August 2026. Its rows go up in 500 g steps to 2 kg, then in 1 kg steps to 5 kg, and then there is a rate for every additional kilogram. Its columns are Local, Within State, Zone / Metro and Other States.

Amazon.in's fees and pricing page sets a minimum chargeable weight of 500 g for standard-size items and charges heavier parcels in 500 g steps. Its own example is an 800 g package, charged as the first 500 g plus the next 500 g. Its distance tiers are local, regional and national.

Notice that the slab width does not always stay the same down the card. On the India Post table, it doubles after 2 kg, which moves every cliff after that point.

I would read the notes before the grid. The grid gives you the price of each slab. The notes decide which slab you are in.

Why does the price jump in steps instead of rising smoothly?

Think of paid parking that charges by the hour. Stay 61 minutes, and you pay for two hours. Most of us have paid for that extra minute at least once.

Courier slabs work the same way. The phrase you will see on many cards is "or part thereof", which means any part of a slab is charged as a whole slab.

Blue Dart's conditions of carriage spell it out. For its Domestic Priority service, section 6.1 rounds both the actual weight and the volume weight up to the next half kg or 1 kg, depending on the rate category agreed, and charges the higher of the two.

For senders like us, two things follow from this.

1. The higher weight picks the slab. For a light, bulky product, that is usually the volumetric weight: the box volume divided by the courier's divisor, which is 5000 for most express services in India.
2. The rounding comes after that choice. A parcel at 0.51 kg pays for 1.0 kg, exactly like a parcel at 0.99 kg.

The first slab usually costs the most, and there is a reason for it. Picking up a parcel, sorting it and delivering it to a door costs the courier about the same for 100 g as for 450 g. That fixed work sits in the first slab. Each additional slab pays mainly for extra weight, so it is normally priced lower.

How much lower depends on your card. That difference decides how hard a cliff hits you.

Which cliff hurts the most?

The first one. I would look there before anywhere else.

Let us show it with index numbers instead of rupees. We call the first-slab charge 100 and each additional slab 85. These are not any courier's rates. They only show the proportions, so put your own card's figures in their place.

Crossing from the first slab into the second adds 85%. That is the "nearly double".

At the 3 kg line, the same additional slab adds only 19%, because it sits on top of a bigger bill.

The jump at any line is the additional-slab charge divided by what you were paying before. At the first line, it is A ÷ F, where F is the first-slab charge and A is the additional-slab charge. The closer your card prices A to F, the closer the first cliff comes to doubling your bill.

This is why small parcels feel the cliffs most. A seller of earrings or tea samples lives near the first line. A seller of bedsheets lives further down the card, where each step is a smaller percentage of the bill.

How can one inch cross a slab line?

Many carton makers in India still quote box sizes in inches, while courier formulas work in centimetres. So let us write the rule both ways, at a divisor of 5000.

1. In centimetres, each extra centimetre on one side adds (the other two sides multiplied together) ÷ 5 grams of volumetric weight. A 40 × 30 cm face gains 240 g for every centimetre of height.
2. In inches, each extra inch adds about 3.3 g for every square inch of the other two sides, because one cubic inch is 16.39 cm³.

Here is what one more inch adds on some common carton faces, which we worked out at the same divisor.

Look at the 14 × 11 row. From a face of about 1,000 cm², one inch adds more than a full 500 g slab. If volumetric weight decides your bill, that inch crosses at least one line wherever you start.

On smaller faces, it depends on where you start inside the slab. I call that the headroom, and the worked example below shows how to find it.

On a surface service with a smaller divisor, the same inch adds even more weight.

Can a few grams do the same?

Yes, when the actual weight is the higher one.

A dense product packed at 480 g has 20 g of headroom. A heavier carton grade, a second copy of the invoice, an extra wrap of tape or a free sample can take it past 500 g, and then it bills as 1 kg.

Near a slab line, the packaging grams we usually ignore stop being small change. Ask the person who packs your best sellers to weigh the empty carton, the void fill and the tape for each one, and write the figures down. A lighter carton or a thinner film can bring a borderline parcel back under, and our guide to downgauging explains how to do that without losing strength.

I will be honest here. Most parcels are nowhere near a line, and for them, shaving grams is not worth a meeting.

Find the few that are close, and work on those.

Do zones change the size of the jump?

Yes. Every column on the card has its own price for each row, so the same inch costs a different amount depending on where the parcel goes.

You do not choose the zone. Your customer's pin code does.

So we work out the cost of a cliff from the zone mix.

Take the share of last month's parcels that went to each column, multiply each zone's additional-slab charge by its share, and add them up. That is your average cost of crossing one line.

Ask your courier, or your shipping aggregator, for the list of pin codes in each zone. Without it, you cannot read the columns properly. I would ask for it in writing, together with the divisor and the slab size.

Where do size limits and oversize charges come in?

Slabs are small steps. Size limits are bigger ones.

Cross them, and you leave the normal table, either for a separate price list or for a fixed surcharge on top. Here are three published examples. I checked all three on 22 October 2026.

1. DHL Express in India adds a fixed Oversize Piece surcharge to any piece whose longest side exceeds 100 cm or whose second-longest side exceeds 80 cm. Above 70 kg, actual or volumetric, the Overweight Piece surcharge applies instead. Its surcharges page was updated on 27 June 2026, effective 1 August 2026, and its fuel surcharge, a percentage of the transport charges, applies to these surcharges as well.
2. India Post accepts a Speed Post parcel up to 1.5 metres long, with length and girth together up to 3 metres and a gross weight up to 35 kg, as per the same Speed Post Parcel page.
3. Amazon.in moves an item into its Heavy & Bulky tier if the packed item weighs more than 22.5 kg, its longest side is more than 183 cm, or its girth is more than 300 cm. Amazon defines girth as length plus twice the sum of width and height.

So a carton at 101 cm can cost far more than one at 99 cm, although no customer would ever notice the difference. We export to 20+ countries ourselves. If you export bulky goods too, put these lines on your carton drawing before you put a freight figure in a quotation.

How do you find the cliffs on your own rate card?

This takes about an hour, once. Sit with your rate card, your rate agreement and last month's dispatch data.

1. Write down the divisor and the slab size for each service you use. Mark any row where the slab width changes.
2. List the slab tops: 0.5 kg, 1.0 kg, 1.5 kg and so on.
3. Multiply each slab top by the divisor. That is the largest box volume that stays inside the slab. At 5000, the lines sit at 2,500, 5,000, 7,500 and 10,000 cm³.
4. Note the size limits and oversize triggers from the terms.
5. For your 10 best sellers, put the packed weight and the box volume next to those lines. My own rule is to flag any product within 10% of a line, above or below.
6. For each flagged product, work out how many millimetres or grams it can move before it crosses a line, in both directions.

I would start with the products just above a line, because that is where the saving is.

The products just below a line are where the risk is.

Your calculation

Let us say we sell a Diwali dry-fruit gift box. Every figure in this example is assumed, chosen only to show the arithmetic.

1. We pack it at 420 g in the shorter carton and 440 g in the taller one.
2. Our courier uses a divisor of 5000, with 500 g slabs.
3. Our charges follow the index from above, with the first slab at 100 and each additional slab at 85.

One inch of height moved our parcel from the first slab to the second. The charge went up by 85%.

Now let us look at the headroom on Carton A. Its line is 2,500 cm³, and it uses 2,360 cm³. Spread the remaining 140 cm³ over its 8 × 6 inch face, which is about 310 cm², and you get roughly 4.5 mm of height.

So Carton A passes, but only just. A lid that bulges by 5 mm can take it over the line. I would keep this product in Carton A, pack it so the lid closes flat, and check a few parcels every week of the festive season.

Now put rupees in. Say your card's additional-slab charge, averaged over your zone mix, is ₹R. If we send 1,500 gift boxes in Carton B during the Diwali month, the extra inch costs us 1,500 × R. At an assumed R of ₹40, that is ₹60,000 in one month.

This is the sheet we would build to repeat it. Keep one row per product, with L, B and H in cm, D as the divisor, S as the slab size in kg, and F and A from your card.

1. Chargeable weight in kg: = CEILING(MAX(actual, L*B*H/D), S)
2. Charge: = F + (chargeable/S − 1) × A, for as long as the slab width stays the same
3. Volume left before the next line, in cm³: = chargeable × D − L*B*H
4. Height left before the next line, in mm: = volume left ÷ (L × B) × 10
5. Grams left before the next line: = (chargeable − actual) × 1000
6. Monthly cost of crossing one line: = parcels per month × your zone-weighted A

Run the same rows backwards for products just above a line. The volume you must remove, divided by the face, tells you how much to take off the shortest side.

One caution before you cut. A box with no room for cushioning saves one slab and can lose you a product. Our worksheet on what a damaged delivery costs shows how to weigh one against the other.

Take your rate card out this week. Find the first line, write down A ÷ F, and check which of your best sellers sits within a few millimetres of it. If you want a second pair of eyes, send us your box sizes, packed weights and slab size through the contact page, and we will mark the cliffs with you.