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Drawers - Kitchen
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Shelf Sag Calculator

A precise, modern alternative to the classic Sagulator for load calculations.
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Calculated projects: 0
Need help with the terms?
Practical tips and quick search in the knowledge cards are waiting below.
How will the shelf be loaded?
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What is the shelf made of?
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Different materials have different stiffness (modulus of elasticity). Solid wood holds more than particleboard.
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Expert Settings
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Mounting type
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Fixing the shelf at the ends (e.g., with screws) significantly reduces sag compared to resting on pins.
Stiffening Lip (Edging)
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Adding a vertical lip (edging) to the shelf drastically increases its load capacity.
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Shelf Sag Calculator & Calcwood Project

Watch a quick video introducing the entire Calcwood project and explaining why these tools are created. The video includes English subtitles (other languages available in player settings).

What can this calculator do?

  • Time-based calculation: Simulates material creep. You will get a technical estimate for installation, 5 years, and 10 years after.
  • Wide range of materials: Supports calculations for particleboard, MDF, OSB, plywood, and solid wood (soft and hard).
  • Two load modes: Uniform load (e.g., books) or point load (e.g., heavy machinery or TV).
  • Safe capacity: Reverse calculates the maximum load a shelf can handle while staying within aesthetic limits.
  • Mounting & Reinforcement (PRO): Simulation of fixed side mounting or adding a reinforcing lip (cleat) to the edge.
  • Interactive visual preview: Instant update including an exaggerated sag curve for better visualization of deformation.
  • PDF Export: Download results as a clean technical sheet for your project.

Basic Rules and Physics of Shelf Sag

Designing shelves is not just about looks, but about understanding how material behaves under load over time. Here is an overview of key terms:

Immediate SagDeformation that occurs immediately after loading. It is the starting point for all further time-based calculations.
Material CreepA phenomenon where wood and boards sag more and more under permanent load. For laminate, it can be triple after 10 years.
Limit Sag (L/300)Standard for an "aesthetically straight" shelf. Sag should not exceed 1/300 of the length (e.g., max 3mm for 900mm).
Reinforcing Lip (Cleat)A vertical strip on the edge. Even a small lip on the front or back can radically increase stiffness and load capacity.
Mounting TypeA loose shelf sags much more than a shelf that is firmly fixed (screwed) into the cabinet sides.
Back PanelIf you screw or nail the shelf to the back panel, sag in that area is practically eliminated, increasing overall capacity.
Grain DirectionFor solid wood and plywood, grain must run along the shelf length (support to support). Transverse capacity is dramatically lower.
HumidityIn humid environments (basements, bathrooms), material creep accelerates significantly. This tool assumes a dry interior.
Support LimitsThe calculation only covers the shelf sag. Remember that shelf pins, cabinet sides, and wall plugs must also handle the total weight.

⚠️ Disclaimer: This calculator is a technical tool for estimating material behavior. Results are based on structural principles (e.g., Eurocode 5) but do not replace a professional structural assessment.

How does the calculator compute sag over time? (Physics Behind It)
Wood and board materials have a specific property – under permanent load, they undergo creep. This means that a shelf sags more and more over time under the weight of books or dishes. While solid wood is more stable, materials like particleboard (LDF) or MDF can have significantly higher long-term deformation. This tool simulates these physical processes for a 5 and 10-year period.

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UPDATES & CHANGELOG
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v1.14 ( October 2026)
  • Units in every language: You can switch between metric and imperial units in every language version of the calculator.
  • Settings preserved: Switching units preserves the material, load mode, expert settings and manually entered dimensions. Unchanged values return without losing precision.
  • Clear manual changes: User-modified values are highlighted in yellow, making it easy to see which inputs differ from their defaults.
v1.13 ( October 2026)
  • More precise dimension entry: I added linked sliders for shelf span, depth, and thickness. You can quickly adjust a value with the slider or enter it precisely in the number field.
  • Invalid input protection: The calculator now checks permitted dimension and load ranges more clearly. It highlights invalid values and blocks the calculation until they are corrected.
  • Clearer controls: I improved the layout of material thickness, load type, and total load controls for easier use on both desktop and mobile devices.
  • Improved drawing: I made the time-based sag visualization at installation, after 5 years, and after 10 or more years easier to read. Sag and strength warnings are now assessed separately so the drawing explains the shelf behavior more clearly.
  • I preserved support for metric and imperial units, US fractions, shared links, and saved configurations.
v1.12 ( June 2026)
  • Added full fraction support for the imperial system (inches). When you switch the calculator to inches, all results and PDF exports are now automatically displayed in easy-to-read fractions (up to 1/16 inch precision).
  • Decimal numbers entered as input are automatically converted to the nearest practical fraction, making workshop tasks much easier.
v1.11 ( June 2026)
  • URL sharing fix: The sharing link now correctly remembers whether you were calculating a custom load or searching for maximum capacity.
  • PDF export fix: Adjusted the text layout in the PDF report to prevent overlapping when using longer material names.
v1.10 ( April 2026)
  • New materials: I added 7 new materials to the expert settings.
  • You can now calculate sag for HDF, compact boards (CDF/HPL), blockboard, poplar and beech plywood.
  • I separated solid wood into specific species (spruce, pine, oak, beech) for dead-accurate results.
v1.00 ( March 2026)
  • Unique feature: Time-dependent sag modeling. Unlike standard tables, this calculator accounts for material creep. You will see the exact sag at installation, after 5 years, and the final state after 10+ years.
  • First public release of the calculator.
  • Support for particleboard, MDF, plywood, and solid wood.
  • PRO features: Effect of fixed mounting and adding a stiffening lip (edging).
  • Dynamic SVG drawing visualizing the bending curve.
  • PDF report generation and configuration sharing via URL.
Have a suggestion or found a bug? +
📌 FINAL WORDS

Hi! The goal of this tool is to help professionals and skilled makers with their projects. Basic features are and always will be free. Advanced "PRO" settings are paid and help fund the server costs and future development of this service. I hope this calculator saves you a lot of time and nerves!

⚠️ Disclaimer: While I do my best to ensure accuracy, I am not responsible for any errors or miscut materials. Always use common sense and the "measure twice, cut once" rule.

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