How to Calculate Eyeglass Lens Thickness
Understand refractive index, base curve, lens material, and thickness. Includes practical examples and our free calculator.
Calculator Guides
Learn the concepts behind each calculator and get the most accurate results. Step-by-step examples, common mistakes, and pro tips.
Frequently Asked Questions
What are Calculator Guides?
Short, practical articles that explain how to use our calculators, the formulas behind them, and tips to get accurate results.
Which calculators have full guides right now?
We currently feature guides for the Lens Thickness Calculator and BMI Amputee Calculator, with more on the way for construction, finance, real estate, time/date, audio, and sports tools. See Lens Thickness Guide and BMI Amputee Guide.
How do I choose the right lens index for my glasses?
Higher prescriptions generally benefit from higher-index materials for thinner, lighter lenses. Use our Lens Thickness Calculator and read the guide for recommendations by prescription strength.
How accurate are the calculator results?
Our calculators use industry-standard formulas and assumptions. Results are estimates for education and planning. For medical, legal, or financial decisions, consult a licensed professional.
Can I use these calculators on mobile?
Yes. All calculators and guides are optimized for mobile and desktop so you can get results anywhere.
Where do I find all calculators by category?
Visit the Categories page to browse every calculator by topic, including construction, finance, real estate, optics, audio, sports, and more.
Featured Step-by-Step Guides
How to Calculate BMI for Amputees
Use adjusted body mass calculations for amputees with correct percentage reductions. Includes charts and examples.
Construction & Home Improvement
TEC Grout Coverage Guide
Estimate grout needed by tile size, spacing, and area. Learn best practices and avoid under/over buying.
Gambrel Roof Dimensions Guide
Plan a barn-style roof: slopes, run, rise, and materials. Visualize dimensions and get material estimates.
Paver Base Depth & Materials
Calculate base depth, gravel, and sand requirements for patios and driveways with pro recommendations.
Tree Removal Cost Factors
Estimate cost by height, trunk diameter, and complexity. Learn typical price ranges and add-ons.
Finance & Real Estate
Chatham Rate Cap Basics
Understand interest rate caps, breakevens, and risk management. Run scenarios with your variables.
Net Effective Rent Explained
Account for concessions and free months to compare leases apples-to-apples with clear outputs.
Moore–Marsden Community Interest
Estimate community share of home equity with down payment and appreciation under California case law.
Science, Audio, and Time
Time Math: Past and Future
Compute what time it was or will be with additions/subtractions in hours and minutes. Common examples included.
RPM ↔ FPM Conversion
Convert between rotations per minute and feet per minute with context for machining and manufacturing.
Tone Stack Frequency Response
Visualize EQ curves for classic guitar amp circuits. Learn how component values shape the response.
Dunk Calculator: Can You Dunk?
Estimate your vertical reach and the gap to the rim with practical training insights.