Roofing Calculator Materials. Roofing calculations require pitch and area. Formula: Squares equals Roof Area divided by 100. Roofing sold in squares (100 sq ft). Calculate area: Length times Width times Pitch Factor. Pitch factor accounts for slope: flat equals 1.00, 4/12 pitch equals 1.054, 6/12 equals 1.118, 8/12 equals 1.202, 12/12 equals 1.414. Example: 40 foot by 25 foot roof with 6/12 pitch. Area 1,000 sq ft times 1.118 pitch equals 1,118 sq ft equals 11.18 squares. Add 10 percent waste equals 12.3 squares, buy 13 squares. Shingle types: 3-tab basic, cheapest, 20-25 year life, 1-3 per sq ft installed. Architectural (dimensional) most popular, 25-30 years, 3-5 per sq ft. Premium designer 30-50 years, 5-10 per sq ft. Metal panels 40-70 years, 7-15 per sq ft. Tile or slate 50-100 years, 10-25 per sq ft. Materials beyond shingles: Underlayment (felt or synthetic) 0.25-0.50 per sq ft. Ice and water shield eaves and valleys 0.75-1.50 per sq ft. Drip edge metal 2-4 per linear foot. Ridge cap shingles 5-7 per linear foot. Flashing chimneys and skylights. Ventilation ridge vent 3-5 per linear foot. Nails, starter strip. Cost example 2,000 sq ft roof: 20 squares architectural shingles 2,000, underlayment 750, ridge cap 200, flashing 150, vents 200, materials total 3,300. Labor tear-off 1,000, installation 3,000, total 7,300 or 3.65 per sq ft. Pitch measurement: Rise over run. 4/12 means 4 inches rise per 12 inches horizontal. Steep roofs over 6/12 require extra safety, higher labor cost. Measure from ground: use pitch gauge tool or calculate from attic. Pitch affects materials: steep pitch wastes more shingles 15-20 percent, requires scaffolding, increases labor 25-50 percent. Low slope under 2/12 requires modified bitumen or TPO membrane, shingles inadequate. Roof penetrations: Each skylight requires flashing kit 50-150. Chimneys need custom flashing 200-500. Plumbing vents use boot seals 5-15 each. Count all penetrations, add materials. Valleys: Open valley uses metal 75-150, woven valley uses shingles, closed cut valley fastest. Add 10 percent material for valley waste. Complex roofs: Multiple levels, dormers, hips increase complexity and waste. Simple gable roof 10 percent waste. Hip roof 15 percent. Complex multi-level 20-25 percent waste. Measure each section separately. Common mistakes: Measuring ground floor not actual roof area. Ignoring pitch factor underestimates by 10-40 percent depending on steepness. Forgetting underlayment, flashing, ridge cap. Not accounting tear-off disposal costs 50-100 per square. Assuming DIY safe, roofing dangerous requires fall protection. Pro tips: Use roofing calculator or smartphone app for pitch. Order 10 percent extra shingles for future repairs, discontinued colors impossible to match. Install ice and water shield on all eaves and valleys prevents ice dam leaks. Proper ventilation extends shingle life, install ridge vent plus soffit vents. Never roof over existing shingles more than twice, building codes limit. Remove old roofing for inspection of decking. Roof deck: Plywood or OSB sheathing. Replace damaged sections before new roof 40-60 per sheet installed. Entire re-deck costs 1.50-3.00 per sq ft. Check from attic for water stains, sagging, rot. Permits and codes: Roofing permit required most areas 150-500. Must meet wind rating for region. Fire rating Class A best. Warranty requires professional installation. DIY voids manufacturer warranty. Insurance may cover storm damage. Lifespan and value: Quality roof increases home value 5,000-15,000. Prevents 10,000-50,000 in water damage. Plan replacement every 20-30 years depending on materials. Metal roofs last 40-70 years but cost double. Tile lasts 50-100 years premium appearance. FAQ: How many squares is my roof? Measure length times width times pitch factor, divide by 100. Average house 15-30 squares. Cost to re-roof? 5,000-15,000 depending on size and materials. Can I roof over existing? Sometimes allowed for one layer only, better to tear off. DIY roofing? Possible but dangerous, voids warranties, requires special tools and safety equipment. When to replace? Curling shingles, missing granules, leaks, 20-25 years old.