Solder Per Joint Calculator
Estimate solder per joint, total solder mass, wire feed length, waste, and flux allowance for copper plumbing, electronics, lugs, connectors, and small metal seams.
Choose a starter case, then adjust the geometry. The fillet length is the wetted path around or along the joint.
Solder estimate
| Alloy | Typical use | Density | Notes |
|---|---|---|---|
| Sn99.3/Cu0.7 | Lead-free electronics, some plumbing | 7.31 g/cm³ | Good default for lead-free wire |
| 95/5 Sn/Sb | Potable copper plumbing | 7.28 g/cm³ | Common solid wire plumbing alloy |
| SAC305 | RoHS electronics assembly | 7.38 g/cm³ | Common lead-free PCB alloy |
| Sn63/Pb37 | Electronics repair | 8.40 g/cm³ | Eutectic tin-lead solder |
| Sn42/Bi58 | Low-temperature rework | 8.56 g/cm³ | Use only where compatible |
| Joint type | Best input diameter | Fill range | Typical check |
|---|---|---|---|
| Copper pipe cup | Tube outside diameter | 65% to 85% | Continuous ring at cup edge |
| PCB through-hole | Lead diameter | 30% to 55% | Concave cone, pad wetted |
| SMD gull-wing | Lead or pad width | 25% to 45% | Toe and heel wetted |
| Wire lug | Strand bundle diameter | 55% to 85% | Strands wetted, no bulb |
| Stained glass seam | Bead width | 25% to 45% | Smooth raised bead |
| Wire diameter | Area | Good for | Control note |
|---|---|---|---|
| 0.3 mm | 0.071 mm² | Fine SMD pads | Short feed length per pad |
| 0.6 mm | 0.283 mm² | Through-hole PCB work | Easy dose control |
| 1.0 mm | 0.785 mm² | Lugs and connector cups | Good bench default |
| 1.6 mm | 2.011 mm² | Large wires and small tube | Feeds quickly |
| 2.4 mm | 4.524 mm² | Copper pipe joints | Use steady heat |
| Scenario | Diameter | Fillet path | Waste guide |
|---|---|---|---|
| 1/2 in copper socket | 15.9 mm | 50 mm | 15% to 25% |
| 0.1 in header pins | 0.64 mm | 2.4 mm | 8% to 15% |
| XT style solder cup | 3.5 mm | 8 mm | 10% to 20% |
| 10 AWG lug | 2.6 mm | 12 mm | 12% to 25% |
| Copper foil glass seam | 4 mm | 1200 mm | 15% to 30% |
Solder joints may appear simple to a person, but the amount of solder that remains in the solder joint can be dificult to estimate. A person may find that the solder seems to dissapear more faster than a person expects when purchasing a spool of solder. The difference between a solder joint that hold and fails can be the difference in the amount of solder that is placed within the solder joint.
While it is true that a person can estimate the amount of solder that will be needed for a solder joint, it can become difficult to do so if a person must solder many joint. If a person does not add enough solder to the joint, the solder joint can crack due to not being supplied with enough solder. If a person add too much solder to a joint, the person will waste money on solder and may create blobs of solder that must be removed from the solder joint.
How to Estimate the Amount of Solder You Need
There are various types of solder joints, and each joint require a different amount of solder to complete the task of creating a joint. For example, a copper pipe will use more solder for the cup joint than a PCB that only require a small amount of solder at the lead. Similarly, a wire lug will require more solder than a stained glass joint.
One of the factors that will impact the amount of solder needed is the type of solder alloy that will be used for the solder joints. For instance, lead-free tin-copper solder alloys will weigh different than tin-lead eutectic solder alloys. The density of the solder alloy impact the amount of solder that will be needed for a joint.
A calculator can estimate the amount of solder needed if the person use the correct solder alloy in the parameters of the calculator. Using the proper solder alloy and path length will ensure that the output of the calculator is the correct weight of solder needed for the joint. A person may also have to account for waste when calculating the amount of solder needed for a project.
Most solder joints will not contain 100% of the solder being solid. If the person is working with small printed circuit board pads, they may use less solder than plumbing joints due to the capillary action of the copper. Additionally, the person will have to account for the amount of solder drips that may happen during the soldering process as well as the amount of solder end that may need to be cut off.
By adding waste allowances to the solder calculation, a person can ensure they dont run out of solder for there project. Flux can be used in a soldering task but does not contribute to the amount of solder that form the joint. The soldering task will consume flux but is not part of the solder mass.
A person will have to account for flux separately from the solder calculation. Another way a person can estimate the amount of solder needed for a task is by using reference tables. These tables contains the amount of solder needed for various joint classes and wire sizes.
These tables can show a person the amount of solder waste that can be expected when soldering fine electronics as opposed to plumbing tasks. By using these tables, a person can more easy set the waste allowances for each task. Once a person has an estimate for the amount of solder needed for a task, a person must determine whether the estimate fall within the amount of solder that a person has.
If the task uses most of the solder that a person buy in a spool, a person should of had a second spool of solder prepared before beginning the task. A person should also ensure that the total number of solder joints to be completed is within the number of joints that can be completed with the solder package that a person purchased. While the geometry inputs in a solder calculator are abstract, a person must use real dimensions when preparing the inputs.
The diameter of the solder joint is the actual size of the path or lead where the solder will go. A person can use calipers to measure the size of the joint. The length of the fillet is the distance that the solder will travel to join the components.
If a person use the actual dimensions of the components to be soldered, the solder joint calculation will be accurate and trustworthy. While a person can learn to solder without planning the amount of solder needed for a task, planning the amount of solder needed for a task remove the uncertainty regarding the material needed for the task.
