General Questions
There won't be a downloadable mobile app. CalcWood performs complex background operations (Opticutter cut lists, PDF generation, license verification) that require a server and internet connection. It simply wouldn't work as an offline app. However, I have perfectly optimized the entire website for mobile devices. Plus, you don't need to install any bloatware, and you always have the latest version instantly.
💡 My tip: Open the website in your mobile browser, open the menu, and select Add to Home Screen. It creates an icon on your screen and works just like a native app.
If you are unsure about any input fields, look for the small yellow question marks next to them. These are helpful tooltips. Just hover your mouse over the question mark (or tap it on mobile) to see a detailed explanation of what the specific value means. I highly recommend checking these tooltips before using the calculator.
When printing from your PDF viewer, make sure to select "Actual Size" or "Custom Scale: 100%". Do not use "Fit to Page" or "Shrink to Fit", as this will distort the dimensions.
The basic calculation is free in every calculator. The calculators run directly in your browser on a computer, tablet or phone, so there is nothing to install, and you do not need an account or registration to calculate. Advanced settings, saved projects and other features are unlocked by an optional PRO licence, which you sign in to with a licence key, without creating a password. Calculators marked BETA have their PRO features temporarily unlocked for free during testing.
Yes. The “Copy Link (URL)” button creates a link that contains all your inputs. Anyone who opens it sees the same calculation, and you can return to it at any time. Saving to a personal project archive and calculation history is part of PRO.
PRO License, Account & Payments
The PRO license unlocks all current calculators and other features I continuously add to CalcWood. You get expert settings, detailed PDF plans, and the ability to save projects to your personal archive. You can find all details on the Premium Access page.
After you sign in with your license key, that browser will remember you for up to 365 days from your last visit. You will only need to sign in again after logging out manually, deleting cookies, your license expiring, or using a different browser or device. In private or incognito mode, the sign-in is automatically removed after all private windows are closed.
First, run several free calculations and make sure the input workflow and results suit you. Also review the locked Expert Settings. Even without a license, you can see their labels, available options, and explanatory tooltips. This lets you check exactly what PRO includes before purchasing, and I recommend buying a license only after doing so.
The PRO license is intended for one user. You can keep your account active on up to 5 of your own devices, such as your phone, a workshop tablet, and your home computer. Sharing the license with friends or using it for multiple people in a company is not allowed.
The subscription is billed on a recurring monthly or yearly basis, depending on the selected plan. You can stop future payments at any time through My Account using the "MANAGE SUBSCRIPTION AND INVOICES" button.
Yes. You can cancel your subscription at any time through My Account. Your PRO access remains active until the end of the period you have already paid for.
Your calculation history and saved projects are not automatically deleted when PRO access ends. They remain linked to the email address used for the purchase. If you reactivate PRO later with the same email address, your previous data becomes available again after you sign in. Data linked to a different email address is not transferred automatically.
Yes. Open My Account and select "MANAGE SUBSCRIPTION AND INVOICES". This opens the secure Stripe customer portal, where you can download the relevant payment documents.
Because this is a digital service that unlocks immediately after purchase, please try the free features first and make sure the calculators suit your workflow. If you encounter a serious technical problem, contact me and I will handle it fairly based on the specific situation.
Heat Loss Calculator
The calculator compares the heat loss of the specified structure with and without added insulation. It multiplies the difference by your energy price to show the annual savings. The Return on Investment (ROI) is calculated by dividing the total insulation cost by these annual savings. This gives you an estimate of how many years it will take for the investment to pay off.
Dew point is the temperature at which air moisture condenses into water. If the structure is designed poorly, moisture can condense in sensitive areas and eventually cause mold or material degradation. Properly designed external insulation helps move the risk of condensation outside the sensitive parts of the structure.
Thermal transmittance (U-value) indicates how much heat escapes through the structure. The lower the U-value, the better the insulation. Thermal resistance (R-value) works the opposite way – the higher the R-value, the better the structure resists heat loss.
No. This calculator is for a quick estimate and material comparison (it calculates heat transfer through an ideal structure). In a real house, windows, roof, ventilation, and thermal bridges play a huge role. For official certificates and subsidies, always contact a certified engineer.
Yes. Enter the area that still has no added insulation. The calculator shows the current state and how much energy and money insulating the remaining part would save.
In timber structures, it is crucial how the complete assembly manages moisture and how it can dry. EPS can significantly affect this behaviour, so the design of the entire assembly, its vapour control layer, construction details and workmanship all matter. The calculator warns you not to assess the construction from thermal values alone. It calculates heat loss, not moisture movement, condensation or the safety of the assembly; these must be assessed separately.
Drawer Calculator
CalcWood Master checks the specific calculated result using fixed rules linked to the entered dimensions and selected hardware. It can highlight drawers that are too wide, unsuitable slide load capacity, or unused space below the drawers, and recommend what to adjust or verify before manufacturing. It is not artificial intelligence and does not replace the final dimension check. It is a practical rule-based check designed to reveal risk areas before you cut the material.
If you already have a built cabinet and know the exact inner space (clearance), it's easy. Enter your inner dimensions into the main fields for outer width and height, and set the "Cabinet Mat. Thickness" to 0. This tricks the calculator into not deducting anything, and it will calculate the drawers perfectly for your opening.
Opticutter is an integrated tool that calculates a highly efficient way to cut your parts from a sheet of material. Depending on settings, it also accounts for edge banding and saw blade thickness.
I use a smart deduction system. For drawer fronts, the edge thickness is deducted from all 4 sides (2x thickness). However, for cabinet parts and drawer boxes, it is only deducted from the visible front edges (1x thickness) to maintain the exact lengths required for the hardware.
Blum undermount slides are designed for a maximum drawer side thickness of 16 mm. I know some woodworkers use 18mm material and route the bottom edge. However, if the calculator allowed this workaround, it would mess up the lengths of your front and back drawer pieces. To ensure your cut list doesn't get messed up and the drawer can be assembled normally, the app sticks to the official limit.
Overlay fronts create a dead space under the drawers. Normally, inner boxes are made the same height for interchangeability. But if you extend them downwards, you get maximum space. The calculator can do this automatically - just select "Maximize drawer capacity" in the Expert Settings.
The most common mistake is poor squareness. Always measure both diagonals when assembling the drawer box. They should be as equal as possible – ideally within one millimeter. The inner cabinet width (LW) also plays a role – if you are off by more than 1 mm, the slides will rub.
The standard gap is 2 to 3 mm. A workshop trick: Take a standard deck of playing cards, divide it exactly in half, and place them on the left and right (or top and bottom). This centers the front perfectly without complex measuring.
Slides are manufactured in standard lengths (usually in 50 mm increments). If you have a non-standard depth (e.g., 470 mm), go for the nearest shorter one (450 mm). Golden rule: the entire drawer with the slide must be 10–15 mm shorter than the inner clear depth of the cabinet so it doesn't hit the back.
An overlay front covers the cabinet edges and easily hides minor inaccuracies. An inset front is flush with the cabinet edge – it looks premium but requires absolutely precise assembly and a perfectly square cabinet.
Yes. In the “Individual FRONT Heights” section, enter the required height for that drawer and the calculator automatically distributes the remaining space between the others. Fronts, drawer boxes and the cut list are recalculated together. Individual heights are part of PRO.
No. Enter how many cabinets you are building in the “Number of Identical Cabinets” field and the calculator multiplies all parts in the cut list by that number. This feature is part of PRO.
Stairs Calculator
You probably forgot to shorten the first step. The bottom cut of the stringer must always be shortened by exactly the thickness of the tread. The calculator deducts this value automatically so all steps end up the same height after the treads are installed.
The throat is the narrowest part of the stringer left after cutting the notches. For standard interior loads, carpenters recommend keeping at least 115–120 mm of solid wood. If the throat is narrower, the material might not handle the load and could crack. For load-bearing or public stairs, always consult a structural engineer.
The basis is Lehman's formula (ideal step): 2x riser height + 1x tread depth = approx. 630 mm (24.8"). The riser should be 170–180 mm, the tread 270–290 mm. If you go above 200 mm for the riser, the stairs become very steep. The calculator monitors ergonomics automatically.
Yes. The calculator provides two design methods. Automatic mode calculates the effective tread depth from the total rise, ergonomics, and available run. Fixed Depth mode lets you enter the overall physical tread board depth, including the nosing. The calculator subtracts the nosing to determine the actual stringer going and checks whether the complete staircase fits within the available run. If it does not fit, the calculator keeps your board depth unchanged and shows the required run instead.
When planning, don't forget your head! The vertical distance between the step edge and the ceiling above it should be enough so you don't hit your head when walking down – usually, at least around 2100 mm (82.7") is recommended for comfortable clearance.
The overhang (usually 20–30 mm) increases the total tread area. On steeper stairs, it significantly helps when walking down, as the heel has more room to step safely.
Yes. Enter the total floor-to-floor height and the maximum length the stairs may take up. Using Blondel’s rule, the calculator proposes the number of steps, the riser height and the tread depth, and shows a drawing of the stringer. If the ideal step does not fit the space, it reduces the tread depth and warns you that the stairs will be steeper.
Yes. Choose the “U-shape (Two flights)” type and enter the landing depth. The result applies to one flight, so you make two identical stringers. The stair type setting is part of PRO. While the stairs calculator is in BETA, it is temporarily unlocked for free.
After the calculation, it checks how much wood remains below the cut notches of the stringer, whether the stringer is very long, whether the step is comfortable and the pitch reasonable, and warns you if the ideal step did not fit the space. It is an indicative workshop check, not a structural calculation or a building code assessment.
Mix Ratio Calculator (Epoxy, Lacquer)
An exothermic reaction occurred. Epoxy generates heat as it cures. A layer that is too thick or a large volume left in a cup can overheat dangerously. Only mix as much material as you can process within the pot life, and stick to the maximum layer thickness according to the technical data sheet.
Never confuse weight and volume ratios! The components (resin and hardener) often have different densities. This means 100 ml of resin might not weigh 100 g. If the densities are entered correctly or available in the database, the calculator will convert it automatically.
You didn't mix it properly. Unmixed material often stays at the bottom and on the sides of the cup. Use the "two-cup rule" – after the first thorough mix, pour the mixture into a second clean cup and mix again. This significantly reduces the risk of sticky spots.
Most often, this is caused by wood moisture or air escaping from pores. The wood should ideally have 8–12% moisture. Before the main pour, always brush the edges with a thin layer of epoxy (seal coat). This seals the wood and significantly reduces the risk of bubbles.
Pot life shortens with volume. A large volume mixed in a cup hardens and heats up much faster than a thin layer poured on a table. Always mix only as much material as you can comfortably process.
Choose the calculation by dimensions and enter the area and pour height. The calculator works out the required amounts of parts A and B from the manufacturer’s ratio. It warns you when you exceed the recommended maximum thickness of a single layer, and for very small amounts it warns that such a batch cannot be mixed accurately.
Choose the calculation by area and enter m² and the number of coats. The calculator works out the amount of both parts. With PRO it also splits the mix into batches by mixing cup size and calculates the cost including waste. While the mix calculator is in BETA, these features are temporarily unlocked for free.
Shelf Sag Calculator
Wood-based materials (especially particleboard/MDF) "creep" and deform over time under sustained loads. What looks straight today might sag heavily in 5 years. If your result shows a bad sag, the best trick is to add a vertical stiffening lip under the front edge, or screw the shelf firmly to the sides instead of resting it on pins.
The best trick is to add a vertical stiffening lip (apron) underneath or at the front of the shelf. Another option is to screw the shelf firmly to the sides and back of the cabinet instead of just resting it on shelf pins.
Absolutely! The grain must always run along the length of the shelf (from support to support). If you cut the board so the grain runs across, the material's load-bearing capacity will be dramatically lower, and the shelf can easily break under load.
As a rule of thumb, a sag limit of L/300 is often used for an "aesthetically straight" shelf. This means the sag shouldn't exceed 1/300 of its length (e.g., for a 900 mm shelf, the max is 3 mm). The calculator monitors this limit and warns you visually.
Switch to “Calculate max capacity”. The calculator works backwards to find the largest load that keeps the sag within the aesthetic limit of L/300, including material creep over time.
Besides sag, the calculator also gives an indicative estimate of the board’s own strength. It warns you when the reserve is near the limit or when the estimated limit is exceeded. Shelf pins, brackets, cabinet sides and wall plugs are not part of the calculation and must carry the load as well.
Even Spacing Calculator
A cumulative error occurred. Never measure from piece to piece (from slat to slat). Every millimeter of inaccuracy adds up. The calculator generates continuous running dimensions – you pull the tape measure once, lock it, and just make marks.
In the calculator, you can play with the edge offsets. Set symmetrical edges so that you end up with a full slat or an equal gap on both sides. The visual balance of the start and end determines whether the work looks professional.
It is an absolutely crucial dimension for drilling holes (e.g., for dowels or screws). Center-to-center spacing is often more important in structural joints than the actual gap between the materials.
The calculator has three modes. “I have item count” calculates the gap. “I want a specific gap” calculates the number of items. “I want a specific center spacing” calculates the number of items so that the spacing stays exact, and centres the whole layout.
Yes. Enter an item width of 0 and the calculator will calculate centre positions only, for example for screws, drilled holes, dowels or mounting points. The results, the preview and the PDF then show the centre marks.
Safety & Responsibility
The calculator works from the values you enter and the rules built into the app, but the old rule "measure twice, cut once" still applies. Always double-check your dimensions before cutting into expensive material. The app is a great helper, but you are responsible for the final cut.
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