Gross, tare and net weight: how to compute scrap weight

A summary, not legal advice. Checked October 7, 2026.

Net weight is gross weight minus tare. Gross is the scale reading with the sack, drum or truck included. Tare, or tara, is the weight of that empty sack, drum or truck. Net is what you pay for or get paid for. Example: a sack of karton that reads 62 kg in a 2 kg sack is 60 kg net. Deductions for moisture or dirt come off the net.

Below are worked examples for the ways junkshops actually weigh, the deductions buyers take, and what the law says about your timbangan. All numbers in the examples are made up and rounded to keep the arithmetic easy.

What do gross, tare and net weight mean?

• Gross weight: the total weight of a product and its packaging, or of a vehicle with its load, fuel and people.
• Tare (tara): the empty weight of a container. The Tagalog word tara is borrowed from Spanish and means the same thing: the weight of the empty container, used to find the weight of what is inside.
• Net weight: the weight of the product without the tare.

So the formula has two forms. Net equals gross minus tare. Gross equals net plus tare. If you know any two, you can work out the third. Every dispute about weight comes down to one of three things: a wrong gross reading, a wrong or forgotten tare, or a deduction nobody agreed on.

How do you compute net weight for sacks and containers?

Weigh each empty container yourself, write its tara down, and take it off the gross. Do not assume a standard sack weight. A wet sack, a drum with dirt in the bottom or a basket with a broken handle replaced by wire all weigh more than you think.

Example, three sacks of karton:

• Sack 1 reads 48 kg, sack 2 reads 52 kg, sack 3 reads 45 kg. Total gross is 145 kg.
• Each empty sack weighs 1 kg. Total tare is 3 kg.
• Net is 145 kg minus 3 kg, which is 142 kg. That is the weight you price.

Example, copper wire in a plastic drum: the drum with wire reads 38 kg and the empty drum weighs 8 kg, so the net is 30 kg of tanso. If you forget the drum, you pay for 8 kg of plastic at the copper price.

How does truck weighing at a weighbridge work?

When you deliver to a trading company with a truck scale, the truck is usually weighed twice: loaded on the way in, which gives the gross, and empty on the way out, which gives the tare. The difference is the net load.

Example, one material: the truck weighs 9,450 kg loaded and 5,200 kg empty. The net load is 4,250 kg.

Example, a mixed load: the buyer weighs the truck after each material comes off.

• Truck arrives loaded: 9,450 kg.
• After unloading the bakal: 6,950 kg. Bakal is 9,450 minus 6,950, which is 2,500 kg.
• After unloading the karton: 5,200 kg. Karton is 6,950 minus 5,200, which is 1,750 kg.
• Check: 2,500 plus 1,750 is 4,250 kg, the same as the whole net load.

Keep the truck the same for both weighings. Gross vehicle weight includes fuel and people, so the driver and helpers should be in or out of the cab both times, and nothing such as a spare tire, tarpaulin or tools should be taken off between readings.

Then compare the buyer's net with your own. Example: you weighed 4,300 kg at your yard and the trading company accepted 4,250 kg. The 50 kg gap is about 1.2 percent of your weight. Agree with your suki buyer what gap is normal, and chase anything bigger.

What if you weigh the load in several batches?

Junkshop scales are often small. The 2024 Iloilo City junkshop study by Central Philippine University researchers found one to three scales per shop, with capacities from 10 kg to 150 kg, so a big load gets weighed in batches. Record every gross reading and every tare, then add them up.

Example, tanso weighed four times in the same 3 kg basket:

• Readings: 41 kg, 39 kg, 44 kg and 36 kg. Total gross is 160 kg.
• The basket was on the scale four times, so the tare is 4 times 3 kg, which is 12 kg.
• Net is 160 kg minus 12 kg, which is 148 kg.

The common mistake is to take the basket off only once: 160 kg minus 3 kg gives 157 kg, and you pay for 9 kg of copper that does not exist. Decide how you round each reading, to the nearest whole kilo or the nearest tenth, and use the same rule every time.

What deductions do buyers take on top of tare?

Tare covers the container. Buyers often take further deductions for what is mixed into the material. Described generally, the usual ones are:

• Moisture: wet karton, dyaryo or sacks of cans that have been rained on.
• Dirt and sand: soil in bakal, sand in bottles, mud on yero.
• Attachments: plastic or rubber on copper wire, iron screws in aluminum, caps and labels on bottles, other materials stuck to the main one.
• Rejects: pieces the buyer will not take at all. In the Iloilo study, junkshops sorted every delivery into recyclables and rejects before weighing, and handed the rejects back to the seller.

Example: 1,000 kg net of karton with a 5 percent moisture deduction is paid as 950 kg. The 5 percent is only an example. Ask how each buyer measures its deductions, whether by eye, by a percentage or by re-weighing after sorting, and write the deduction on the ticket as its own line, separate from the tare. When the same buyer deducts more and more over the months, that line is how you will see it.

Does your timbangan need to be sealed?

Yes, in most places. Under the Consumer Act (RA 7394), the provincial, city or municipal treasurer enforces the rules on weights and measures, and the Department of Trade and Industry enforces the use of the metric system. Article 62 says every instrument used to determine weight in consumer and consumer-related transactions must be tested, calibrated and sealed every six months by the official sealer, who is the treasurer or an authorized representative, on payment of the fees.

Article 64 lists what is prohibited. It includes using an unsealed scale, or one whose seal has expired, when you buy and sell by weight; altering a scale after it has been sealed; knowingly using a false scale; and giving short weight or misrepresenting the weight of what is bought or sold. Under Article 65, using an unsealed scale carries a fine of at least ₱500 or imprisonment of one month to five years, or both, for a first offense. Altering a scale, using a false scale or misrepresenting weight carries a fine of at least ₱300 or up to one year in prison, or both.

The Local Government Code (RA 7160), in Section 148, lets the local government charge fees for sealing and licensing weights and measures, set rules for their use under guidelines from the Department of Science and Technology, and penalize fraud by ordinance. Offenses that do not involve fraud can be settled with the treasurer through a compromise penalty of at least ₱200.

Cities apply this differently, so check yours:

• Quezon City: its citizen's charter says every person must have scales sealed before using them for business with the public, at the Weights and Measures Unit of the City Treasurer's Office. Bring the application form, your business permit, the scale and your latest official receipt. Listed fees are ₱100 for a mechanical scale of 300 kg and below, ₱150 for one above that, and ₱500 for a digital scale.
• Davao City: the City Treasurer's Office said in June 2023 that a seal on market scales is valid for only three months, with penalties of ₱500 to ₱5,000 or up to six months in prison, or both.

Behind the treasurer's seal is the National Metrology Act (RA 9236), under which the National Metrology Laboratory of the Industrial Technology Development Institute, a Department of Science and Technology agency, carries out calibration work for the country's measurement system.

How do you keep weights you can defend?

• Check that the scale reads zero before each weighing and returns to zero after.
• Weigh each empty container yourself and write the tara on the ticket next to the gross.
• In batches, record every reading, not just the total.
• Write deductions as their own line, with the reason.
• Keep the treasurer's seal intact and the official receipt on file, and re-seal before it expires.
• Test the scale now and then with something whose weight you know, and stop using it if the reading drifts.
• For big or disputed loads, take a photo of the scale display.

ScrapTrack, the junkshop system from Orvyn Solutions, records each purchase at the scale as a numbered ticket. The weight can be entered directly, as gross minus tare, or over several weighings, and you can attach a photo of the scale display to the ticket. When you deliver to a trading company, it compares your weight with the weight the buyer accepted and flags the difference. It does not test or seal your scale; that stays with your treasurer's office. A demo is available.

Sources

• Republic Act No. 7394, Consumer Act of the Philippines, Articles 61 to 65, on Lawphil (lawphil.net). Checked October 7, 2026.
• Republic Act No. 7160, Local Government Code of 1991, Section 148, on Lawphil (lawphil.net). Checked October 7, 2026.
• Republic Act No. 9236, National Metrology Act of 2003, on Lawphil (lawphil.net). Checked October 7, 2026.
• Sealing of Weights and Measures, citizen's charter entry, Quezon City Government (quezoncity.gov.ph). Checked October 7, 2026.
• "CTO strengthens info drive on calibration and sealing of weighing scales in markets", June 29, 2023, Davao City Government (davaocity.gov.ph). Checked October 7, 2026.
• Romallosa, Penetrante and Ravena, "Junkshops as Recycling Chain Actors in the Recovery of Waste Resources from a Highly Urbanized City in the Philippines", Applied Environmental Research 46(3), 2024, on ThaiJO (ph01.tci-thaijo.org). Checked October 7, 2026.
• Entries "tara" (Tagalog), "tare", "gross weight" and "net weight", Wiktionary (en.wiktionary.org), third-party dictionary. Checked October 7, 2026.