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🔧 Free General Tools

General
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Practical, everyday tools for construction, measurement and everyday maths. Calculate shed roof slopes, convert units, find areas and get accurate answers instantly — no signup, no ads, no nonsense.

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5
General tools
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Imperial & Metric
Unit systems
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All General Tools

5 tools
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Unit Converter
Convert between length, weight, volume and temperature units. Supports metric and imperial. Instant bidirectional conversion.
Used 800 times this month
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Area Calculator
Calculate area for rectangles, circles, triangles and irregular shapes. Supports square feet, metres and more. Great for flooring and tiling.
Used 620 times this month
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Percentage Calculator
Calculate percentages, percentage change, percentage of a total and reverse percentages. Covers discounts, markups and tax rates.
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Concrete Calculator
Calculate how many bags of concrete or cubic metres of mix you need for slabs, footings and posts. Supports standard bag sizes.
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Paint Coverage Calculator
Calculate how many litres of paint you need for any room. Enter wall dimensions, number of coats and coverage rate — get litres and cans.

Free general calculators — how they work

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How does a roof slope calculator work?

The shed roof slope calculator uses the Pythagorean theorem — rafter = √(rise² + run²). Enter any one known measurement (rise, run, angle or pitch ratio) and the calculator derives everything else: wall height difference, rafter line length, eave overhang, true roof surface area, pitch multiplier and how many rafters to order. It also shows framing square settings for cutting perfect rafter angles without a protractor.

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Why roof area differs from floor area

A sloped roof always covers more surface than the floor footprint beneath it. The conversion factor is called the pitch multiplier: √((rise/run)² + 1). At 4:12 it's 1.054, so a 120 sq ft shed footprint needs ~126 sq ft of roofing material. At 6:12 it's 1.118, giving ~134 sq ft. Always calculate material quantities from true roof area — ordering from floor area will leave you 5–12% short.

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Unit conversion made simple

Our unit converter handles length, weight, volume and temperature across all common systems — imperial (feet, inches, pounds, gallons, °F) and metric (metres, kg, litres, °C). It's bidirectional: type either value and both update instantly. Useful for converting construction plans between US and metric, or kitchen measurements between tablespoons and millilitres.

FAQ

General calculator questions

Common questions about roof slopes, rafter lengths, unit conversions and area calculations — answered clearly.

A 3:12 to 4:12 pitch is the sweet spot for most shed builds. It provides reliable drainage, works with all standard materials including asphalt shingles, and doesn't require excessively tall walls. In heavy snow regions, increase to 6:12 or steeper. For simple lean-to shelters using metal corrugated sheeting, 2:12 is workable.
Rafter length = √(rise² + run²) using the Pythagorean theorem. For a 12-foot shed (run = 12 ft) at a 4:12 pitch (rise = 4 ft): rafter = √(4² + 12²) = √(16 + 144) = √160 ≈ 12.65 feet. This is the line length from wall to wall. Add your eave overhang (typically 12–18 inches) to get the actual board length needed.
Use the formula: angle = arctan(rise ÷ run). Common conversions: 1:12 = 4.8°, 2:12 = 9.5°, 3:12 = 14.0°, 4:12 = 18.4°, 6:12 = 26.6°, 9:12 = 36.9°, 12:12 = 45°. The shed roof slope calculator above handles this automatically — showing all three formats (ratio, degrees, percentage) simultaneously.
The pitch multiplier converts your shed's floor footprint into the actual sloped surface area for material ordering. Formula: √((rise/run)² + 1). At 4:12, multiplier = 1.054 — a 120 sq ft footprint needs ~126 sq ft of roofing. At 6:12, multiplier = 1.118, giving ~134 sq ft. Always order materials based on true area, not floor footprint, and add 10–15% for waste.
16" on center (OC) is the most common spacing for sheds — it matches standard plywood sheet sizes and gives good structural strength. 24" OC uses less lumber and is fine for lightweight metal or polycarbonate roofing. 12" OC is for heavy loads like thick tile or locations with significant snow. The calculator shows exactly how many rafters to cut for your chosen spacing and shed width.
Yes — completely free, forever. No signup, no email, no premium tier. All Calcgator tools are free to use without any account. Open the tool, enter your numbers and get your result instantly. No ads either.
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