Blind Size Calculator
Calculate blind size easily with our free tool. Get practical results, tips, and comparisons for everyday decisions. Includes formulas and worked examples.
Calculator
Adjust values & calculateFormula
For inside mount blinds, subtract 1/4 inch from both width and height for clearance. For outside mount, add 3 inches (1.5 inches overlap on each side) to both width and height. Check that your window frame depth meets the minimum requirement for your chosen blind type.
Last reviewed: December 2025
Worked Examples
Example 1: Inside Mount Roller Blind
Example 2: Outside Mount for Multiple Windows
Background & Theory
The Blind Size Calculator applies the following established principles and formulas. Everyday life arithmetic underpins a vast range of routine financial and practical decisions that most adults encounter on a daily or weekly basis. At its core, consumer mathematics involves applying straightforward formulas to real-world quantities, but accuracy and convenience are essential when money is involved. Tip calculation follows the simple relationship tip = bill × rate, where rate is typically expressed as a decimal (0.15 for 15%, 0.20 for 20%). When dining in groups, the split total is computed as (bill + tip) / n, where n is the number of diners, though tax is sometimes included before or after the split depending on local convention. Percentage and discount arithmetic is equally fundamental. A discount of 20% on a $45 item is computed as 45 × (1 − 0.20) = $36, and stacked discounts require sequential multiplication rather than addition of percentages. Fuel cost estimation uses the formula cost = (distance / mpg) × price per gallon, allowing drivers to budget road trips or compare vehicle efficiency. Electricity billing relies on unit conversion: kilowatt-hours equal watts × hours / 1000, and the cost is then kWh × the utility rate. A 100-watt bulb left on for 10 hours consumes one kWh, which at a rate of $0.13 amounts to 13 cents. Loan payment calculations typically apply the standard amortisation formula, where monthly payment depends on principal, interest rate per period, and number of periods. Understanding this formula helps consumers evaluate mortgage offers or auto loans without relying solely on lender summaries. Unit price comparison, dividing total price by quantity or weight, is the most direct tool for supermarket decisions and is often more revealing than advertised sale prices. Sales tax, typically a percentage added to a pretax subtotal, varies by jurisdiction and product category. Together, these calculations constitute a practical numeracy toolkit that reduces reliance on guesswork and supports more informed consumer behaviour across every domain of daily spending.
History
The history behind the Blind Size Calculator traces back through the following developments. The history of everyday consumer arithmetic is inseparable from the broader story of commercial society and the gradual democratisation of mathematical tools. In pre-industrial economies, most transactions occurred in kind or relied on weights and measures governed by local custom rather than standardised formulas. The shift toward decimal currency, pioneered by the United States in 1792 and gradually adopted by European nations through the 19th and 20th centuries, made percentage calculations far more intuitive and accessible to ordinary citizens. The rise of the modern supermarket in the mid-20th century created a new demand for practical price comparison skills. Early consumer protection advocates in the 1960s and 1970s pushed for unit pricing legislation, recognising that larger packages were not always cheaper per ounce and that shoppers needed standardised information to compare products fairly. The US Fair Packaging and Labeling Act of 1966 was an early legislative response to these concerns. Personal finance software emerged in the early 1980s as home computers became affordable. Quicken, launched in 1983, was among the first widely adopted tools that automated bill tracking, loan amortisation, and budget projection for ordinary households. It shifted the culture from paper ledgers and mental arithmetic toward software-assisted financial management. The internet era brought free tools and comparison engines that extended these capabilities further. Mint, launched in 2006, aggregated bank and credit card data to provide automatic categorisation of spending, making budget tracking nearly effortless. Smartphone calculator apps, present on virtually every mobile device by 2010, placed instant arithmetic in every pocket. E-commerce platforms subsequently embedded tax calculators, shipping cost estimators, and instalment payment breakdowns directly into checkout flows, normalising real-time financial calculation as part of the purchasing experience. Today, the expectation that digital tools will perform these calculations instantly has become universal, yet understanding the underlying arithmetic remains valuable for interpreting results, catching errors, and making informed comparisons when automated tools are absent or misleading.
Frequently Asked Questions
Formula
Inside Mount: Blind Size = Window Opening - 1/4 inch
For inside mount blinds, subtract 1/4 inch from both width and height for clearance. For outside mount, add 3 inches (1.5 inches overlap on each side) to both width and height. Check that your window frame depth meets the minimum requirement for your chosen blind type.
Worked Examples
Example 1: Inside Mount Roller Blind
Problem: Your window opening is 36 inches wide by 48 inches tall with a frame depth of 3.5 inches. What size roller blind should you order for inside mount?
Solution: Window width: 36 inches\nWindow height: 48 inches\nDeduct 1/4 inch for clearance from each dimension:\nBlind width: 36 - 0.25 = 35.75 inches\nBlind height: 48 - 0.25 = 47.75 inches\nMinimum depth for roller blind: 1.5 inches\nYour depth: 3.5 inches - sufficient!\nArea: 35.75 x 47.75 / 144 = 11.85 sq ft
Result: Order Size: 35.75' x 47.75' | Depth: OK (3.5' > 1.5' min) | Area: 11.85 sq ft
Example 2: Outside Mount for Multiple Windows
Problem: You have 4 windows each 30 inches wide by 60 inches tall. You want outside mount cellular blinds with 1.5 inch overlap on each side. What is the total coverage area and estimated cost?
Solution: Individual blind width: 30 + 3 = 33 inches\nIndividual blind height: 60 + 3 = 63 inches\nIndividual area: 33 x 63 / 144 = 14.44 sq ft\nTotal area for 4 blinds: 14.44 x 4 = 57.75 sq ft\nCellular blind estimate: ~$12/sq ft\nEstimated cost: 14.44 x $12 = $173 each, $692 total
Result: Each Blind: 33' x 63' | Total Area: 57.75 sq ft | Est. Cost: $692 for 4 blinds
Frequently Asked Questions
Is my data stored or sent to a server?
No. All calculations run entirely in your browser using JavaScript. No data you enter is ever transmitted to any server or stored anywhere. Your inputs remain completely private.
Why might my result differ from another tool or reference?
Differences typically arise from rounding conventions, the specific version of a formula (for example, simple vs compound interest), or unit inconsistencies between inputs. Check that both tools are using the same formula variant and the same units. The References section links to the authoritative source behind the formula used here.
What inputs do I need to use Blind Size Calculator accurately?
Each field is labelled with the required unit (metric or imperial). Gather your source values before starting — for example, a weight measurement in kilograms, a distance in metres, or a dollar amount — and enter them exactly as measured. The formula section on this page lists every variable and explains what each represents.
How do I verify Blind Size Calculator's result independently?
The Formula section on this page shows the equation used. You can reproduce the calculation manually or in a spreadsheet using those steps. Compare your answer against the worked examples in the Examples section, which use known reference values so you can confirm the calculator is behaving as expected.
How do I interpret the result?
Results are displayed with a label and unit to help you understand the output. Many calculators include a short explanation or classification below the result (for example, a BMI category or risk level). Refer to the worked examples section on this page for real-world context.
Does Blind Size Calculator work offline?
Once the page is loaded, the calculation logic runs entirely in your browser. If you have already opened the page, most calculators will continue to work even if your internet connection is lost, since no server requests are needed for computation.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy