Guides hub · Updated August 9, 2026

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Direct answer: start here when you need a clear recommendation, comparison, or citeable number — then jump into the matching free calculator. Each guide shows an update date, worked example, and honest limits.

• How-toHow to calculate USPS postageBillable weight (DIM ÷ 166), Priority vs Ground Advantage examples, Flat Rate boxes, and a free postage calculator.
• How-toHow to calculate capital gains tax on a property saleSale − basis − expenses, Section 121 ($250k / $500k), home vs rental examples, and a free calculator.
• How-toWhat is the Wells score for DVT?Nine criteria (−2 to +9), low/moderate/high bands, D-dimer pathway teaching, and a free Wells DVT calculator.
• How-toHow do you calculate the CHA₂DS₂-VASc score?Acronym points, Friberg annual stroke risk %, anticoagulation teaching thresholds, and a free calculator.
• Use caseHow much is scrap metal worth?Direct answer for copper, aluminum, brass, and steel by the pound, with a worked example and calculator.
• Use caseHow much will my TSP grow?Citeable Thrift Savings Plan projections with contributions, match, and compound growth — plus a free calculator.
• Use caseHow much weight will I lose on a water fast?3-, 5-, and 7-day citeable estimates (fat vs water), safety limits, and a free calculator.
• How-toHow do I know my condom size?Measure erect girth, divide millimeters by 2 for nominal width. Worked example: 4.5 in → 57 mm, plus a free calculator.
• Use caseCondom size chart by girthInch and centimeter girth to nominal width in mm, including 4.5 in, 5.5 in, 6 in, and a 60 mm reverse lookup.
• ComparisonFree online calculator sites comparedHonest comparison of The Calcs vs Calculator.net, Omni Calculator, and Desmos — best for, limits, and when to use each.
• How-toHow do I round to the nearest tenth?The hundredths-digit rule with homework answers: 36.89753 → 36.9, 8.329 → 8.3, and more.
• How-toRound a division or square root to the nearest tenth14 ÷ 9 → 1.6, √30 → 5.5, ∛30 → 3.1. Divide or take the root first, then round once.
• How-toNearest tenth vs nearest tenTenth means one decimal place (7,445 → 7,445.0). Ten means the tens place (7,445 → 7,450). Plus percents and negatives.
• How-toHow do I convert feet and inches?12 inches = 1 foot. Convert, add, and subtract ft/in with worked examples and a free calculator.
• Use caseHow many acres is my lot?Acres = square feet ÷ 43,560. Common lot sizes with citeable examples and a free land calculator.
• Use caseHow many lots are in an acre?43,560 ÷ lot square feet. A 5,000 sq ft lot fits 8 whole lots per acre before streets. Six of those lots are 0.6887 acres.
• How-toHow do you convert square meters to acres?Square meters ÷ 4,046.86. One hectare is 2.471 acres. A half mile by a half mile is 160 acres.
• How-toHow do you calculate MME?Daily dose × CDC 2022 factor, then add. Oxycodone 10 mg twice daily = 30 MME/day. Not a switching dose.
• Use caseHow many MME is a fentanyl patch?Patch mcg/hr × 2.4. A 25 mcg/hr patch is 60 MME/day; 50 mcg/hr is 120. Buprenorphine has no factor.
• How-toWhat nicotine patch dose should I start with?More than 10 cigarettes a day: 21 mg for 6 weeks, then 14 mg and 7 mg (10 weeks). Ten or fewer: start at 14 mg (8 weeks).
• Use caseHow many cigarettes is a 21 mg nicotine patch?About 21 cigarettes (one pack), using ~1 mg absorbed per cigarette. Also 14 mg, 7 mg, vaping, and dip.
• How-toHow do you adjust levothyroxine based on TSH?TSH above goal: raise 12.5–25 mcg. TSH below goal: lower 12.5–25 mcg. Recheck in 6–8 weeks. Example: TSH 5.5 on 100 mcg.
• How-toHow many mcg is 0.1 mg of levothyroxine?0.1 mg = 100 mcg. Tablet chart from 25 mcg (0.025 mg) to 300 mcg, plus the 1.6 mcg/kg full-replacement estimate.
• How-toHow is overtime taxed?Same as wages: your bracket plus 7.65% FICA. It is not a higher overtime rate. The 2025–2028 deduction covers only the “half” of time-and-a-half.
• Use caseHow much overtime is tax free?Only the FLSA premium, up to $12,500 ($25,000 joint) for 2025–2028. Phases out above $150,000. FICA still applies.
• How-toHow do you calculate pack-years?Pack-years = (cigarettes per day ÷ 20) × years. One pack a day for 30 years is 30. Add each period if the amount changed.
• Use caseHow many pack-years for lung cancer screening?U.S. low-dose CT uses 20 pack-years, ages 50–80. USPSTF and Medicare also require quitting within 15 years. ACS does not.
• How-toHow does USPS dimensional weight work?Only boxes over 1 cubic foot: L × W × H ÷ 166, rounded up. You pay the higher of actual weight and that number.
• Use caseHow much are USPS Flat Rate boxes?One price to any zone, up to 70 lb. Small box, Medium box, Large box, and envelopes — Post Office vs online.
• How-toHow does the TSP match work?Contribute 5% of basic pay and the agency adds 5%: 1% automatic plus 4% matching. Less than 5% leaves match on the table.
• Use caseHow much can I contribute to the TSP in 2026?$24,500 elective deferral. Catch-up is $8,000 from age 50, or $11,250 at ages 60–63. You plus the agency cannot pass $72,000 before catch-up.
• How-toHow do you find the zeros of a polynomial?Set p(x) = 0, factor, then use the rational root theorem and the quadratic formula. x³ − 15x² + 71x − 105 has zeros 3, 5 and 7.
• How-toHow do you write a polynomial with given zeros?Multiply (x − zero) for each zero. Zeros −2 and 5 give x² − 3x − 10. A complex zero needs its conjugate.
• How-toHow is depreciation recapture taxed on a rental sale?Prior depreciation is unrecaptured Section 1250 gain: ordinary rates, capped at 25%. It cannot be excluded under Section 121.
• Use caseCan I exclude gain if I sell my house before 2 years?Only for a job move, health, or unforeseen event. The exclusion is months qualified ÷ 24 × $250,000 or $500,000.
• How-toHow do you convert bullet drop to MOA?Come-up in MOA = inches of drop ÷ (1.047 × yards ÷ 100). A 6.5 Creedmoor 143 gr ELD-X, 100-yard zero, is about 10.4 MOA at 500 yards.
• How-toShould you use a G1 or G7 ballistic coefficient?Match the number to the drag model. A 6.5 Creedmoor 143 gr ELD-X is G1 0.623 or G7 0.314. Putting 0.623 into a G7 model is the wrong bullet.
• How-toHow do you read a sliding scale insulin chart?Find the glucose row and give that many units of rapid- or short-acting insulin. On the moderate example, 247 mg/dL is 4 units. Below 70 mg/dL, give none.
• How-toHow do you use the 1800 rule for insulin?Correction factor = 1,800 ÷ total daily insulin for rapid-acting insulin. 40 units means 1 unit lowers about 45 mg/dL. Regular insulin uses 1,500.
• How-toHow do you complete a function table?Substitute each input into the rule. For y = 2x + 1 and x from −2 to 2, the outputs are −3, −1, 1, 3, 5.
• How-toHow do you find the function from a table of values?A constant change in y means a line. Outputs 9, 14, 19, 24 for x = 0, 1, 2, 3 give y = 5x + 9. Inputs 4, 6, 7 → 16, 24, 28 give y = 4x.
• How-toHow do you calculate near PD from distance PD?Near PD = distance PD × reading distance ÷ (reading distance + 27 mm). A 64 mm distance PD is 60 mm at 40 cm, not 61 mm.
• Use caseWhat is the average pupillary distance?In the ANSUR survey the mean adult PD is 63.4 mm: 62.3 mm for women and 64.7 mm for men. About 90% of adults fall between 57 and 70 mm.
• How-toHow long does Adderall stay in your urine?A single 20 mg dose stays above the federal 500 ng/mL screen for about 36 hours (22–53 h). Daily 20 mg extends that to about 39 hours. A 50 ng/mL lab test can find it for about 3 days.
• How-toWhat is a normal Adderall level in urine?There is no therapeutic urine range. For 20 mg daily the model expects about 4,910 ng/mL at 4 hours and about 1,360 ng/mL at 24 hours. 7,485 ng/mL is a clear positive a few hours after a dose.
• How-toHow much does it cost to rebuild a house per square foot?About $178 per sq ft nationally in 2026. A standard 2,000 sq ft house is about $356,180 to rebuild. Mississippi and North Carolina are about $144; California is about $219.
• How-toWhat is the 80% rule in homeowners insurance?At 80% of replacement cost, a partial loss pays replacement cost minus the deductible. A $400,000 home insured for $280,000 (70%) pays $42,875 on a $50,000 loss, not $49,000.
• How-toHow much cash value does whole life have after 10, 20, or 30 years?A $100,000 whole life policy bought at 35 for about $1,036 a year holds about $8,730 after 10 years, $25,908 after 20, and $54,679 after 30, at a 6% dividend rate. It breaks even in year 14.
• How-toHow do you calculate life insurance cash surrender value?Add cash value, paid-up additions, dividends, and prepaid premiums, then subtract the loan and any surrender charge. The textbook sum is $1,975. A $50,178.60 surrender with $40,000 of premiums paid has $10,178.60 of ordinary income.
• How-toWhen does ketosis start on a water fast?Liver glycogen is still the fuel for the first 12 hours. The model calls 12–24 hours “entering ketosis” and 24 hours or more “likely in ketosis.” A 3-day fast qualifies; most of the early scale drop is still water.
• How-toHow much water should you drink on a water fast?This calculator budgets 2.5 liters a day: 7.5 L over 3 days, 12.5 L over 5, and 17.5 L over 7. After 48 hours it also flags electrolytes, not plain water alone.
• How-toWhat size lamp shade do I need?Bottom diameter ≈ the base height, within 2 inches. Height ≈ two-thirds of the base. An 18-inch base takes about an 11 × 18 × 12.5 empire shade and an 11.5″ harp.
• How-toWhat does a 9 × 16 × 10 lamp shade mean?Top × bottom × slant: 9 inches across the top, 16 across the bottom, 10 along the side. Vertical height is 9.37 inches. It suits a base about 14–18 inches tall.
• How-toHow do you write a square root in simplest radical form?Pull out the largest perfect square. √72 = 6√2 because 72 = 36 × 2. √24 = 2√6, √12 = 2√3, √8 = 2√2, and √6 is already simplest.
• How-toHow do you add and subtract radicals?Simplify first, then combine only like radicals. 5√28 − 7√7 becomes 10√7 − 7√7 = 3√7. √8 × √24 = 8√3.
• How-toHow do you adjust warfarin based on INR?For a 2–3 target, INR 2.0–3.0 keeps the weekly dose. INR 1.7 on 5 mg daily (35 mg/week) suggests about 37.5 mg/week. INR 3.6 suggests holding one dose, then about 32.5 mg/week.
• How-toHow do you calculate a 10% warfarin dose change?Multiply the weekly total by 0.10. 35 mg minus 10% is 31.5 mg; with 5 mg tablets the nearest even week is 32.5 mg. Going from 44 mg to 47 mg is a 6.8% increase.
• How-toHow much is New Jersey child support on a $120,000 salary?If the other parent has no income, a $120,000 salary is about $392 a week for one child and $445 a week for two. With a $40,000 co-parent, two children are about $371 a week.
• How-toHow does 50/50 custody affect child support in New Jersey?At about 101 overnights (28%) New Jersey switches to the shared-parenting worksheet. At 182 overnights, $90,000 vs $60,000 is about $111 a week for two children.
• How-toWhen is a full truckload cheaper than LTL?Two pallets, 1,500 lb, 900 miles are about $608 by LTL versus $2,730 for a dry van. At 1,000 miles, 20,000 lb on 12 pallets flips: the van is about $3,034 and LTL is about $3,334.
• How-toHow do you calculate freight class from density?Divide pounds by cubic feet. Two 48×40×48 in pallets at 1,500 lb are 14.1 lb/ft³, class 85. On a 1,000 lb, 1,000-mile move, class 50 is about $302 and class 250 is about $1,186.
• How-toHow much do I need to retire according to Dave Ramsey?$10,000 a month, 30 years away, 3% inflation, and an 8% withdrawal is a $3,640,894 nest egg. The same lifestyle at the 4% rule needs $7,281,787.
• How-toHow much is 15% of your income for retirement under Dave Ramsey?Baby Step 4 is 15% of gross pay. On $70,000 that is $875 a month. On $100,000 with a 4% match, the split is $4,000 to the 401(k), $7,500 to a Roth IRA, and $3,500 back to the 401(k).
• How-toHow much does catering cost per person?For 100 guests, $25 of food, 20 miles, and a 20% margin, a buffet is $50.88 per person. Plated is $55.08. A 25-guest buffet is $76.32 because labor and setup stay fixed.
• How-toHow much does catering cost for 100 guests?A buffet with $25 food, 20 miles, and a 20% margin is $5,088, or $50.88 per person: $2,500 food, $600 kitchen labor, $300 equipment, $600 for four servers, and $240 travel and setup.
• How-toHow far should your monitor be from your eyes?A 24-inch monitor at high resolution and medium text is about 56 cm (22.0 in), with a 46–68 cm band. A 27-inch screen is 63 cm. A 32-inch screen is 73 cm.
• How-toHow far should a 27-inch monitor be from your eyes?High resolution and medium text put a 27-inch monitor at about 63 cm (24.8 in), in a 53–75 cm band. Small text is about 63 cm on a standard panel; large text is about 54 cm.
• How-toHow do you convert mg to mL?Divide milligrams by the concentration in mg/mL. For water (1,000 mg/mL), 100 mg is 0.1 mL and 1 mg is 0.001 mL. At 20 mg/mL, 20 mg is 1 mL.
• How-toHow many mg are in a mL?1 mL of water is 1,000 mg. This calculator uses 1,035 mg/mL for milk and 916 mg/mL for cooking oil, so 25 mL of oil is 22,900 mg.
• How-toHow many Trex boards do you need for a deck?A 20 × 12 ft deck at 16 inches on center needs 15 boards. A 10% waste factor raises the order to 17 boards. At 12-inch spacing the same deck needs 20 boards.
• How-toHow much does a Trex deck cost per square foot?A 20 × 12 ft Trex Enhance deck with professional installation is $2,855, or $11.90 per sq ft: $935 in boards and $1,920 labor. DIY leaves the $935 material total.
• How-toHow do you calculate a JWT expiration time?exp = iat + TTL in seconds. Issued at 1735689600 (2025-01-01T00:00:00Z), a 15-minute token expires at 1735690500. One day later is 1735776000.
• How-toHow does clock skew affect JWT expiry?The calculator rejects a token when now ≥ exp + skew. A 15-minute token with exp 1735690500 and 60 seconds of skew stays active until 1735690560.
• How-toHow high should you hang a picture?With a 57-inch eye line, the standard style centers a picture at 58 inches. A 24-inch frame then runs from 46 to 70 inches off the floor. Gallery style centers it at 57 inches.
• How-toHow do you calculate nail height for a picture?Nail height = center + half the frame − hook drop. A 24-inch frame at a 58-inch center with a 4-inch drop needs the nail at 66 inches. A 2-inch drop moves it to 68 inches.
• How-toHow much whipped cream does 1 cup of heavy cream make?1 US cup of heavy cream is about 1.95 cups whipped at medium peaks (about 3.9 half-cup servings). Soft peaks are 1.72×. Stiff peaks are 2.15×.
• How-toHow much heavy cream do you need for whipped cream?Divide the whipped cups by the peak factor. At medium peaks (1.95×), 2 cups of whipped cream need 1.03 cups of liquid heavy cream. Four cups need 2.05 cups.
• How-toHow much does it cost to ship a car?A 1,100-mile open sedan is about $1,675.52 ($1.52 per mile) with a 5-day transit estimate. 500 miles is about $992.87. 2,500 miles is about $3,268.35.
• How-toHow much more is enclosed car shipping than open?Enclosed multiplies linehaul by 1.42. On a 1,100-mile sedan that is $2,100.56 versus $1,675.52 open, a $425.04 gap, and 6 days instead of 5.
• How-toHow does the leading coefficient test work?x³ is odd and positive: as x → −∞, f(x) → −∞, and as x → +∞, f(x) → +∞. x² is even and positive, so both ends go to +∞. A negative leading coefficient flips the ends.
• How-toWhat is the end behavior of a rational function?A higher-degree denominator, as in 1/x and 1/x², sends both ends to 0. Equal degrees approach the ratio of the leading coefficients. A higher numerator follows the quotient polynomial.
• How-toHow much does YouTube pay for 100,000 views?100,000 views at a $6 CPM, education niche, global audience, and 10-minute videos is about $397.80 a month ($3.98 per 1,000 views), or $4,773.60 a year. The band is $278.46 to $596.70.
• How-toHow do you calculate YouTube ad revenue?Revenue = impressions ÷ 1,000 × adjusted CPM. 60% of views count as impressions. $6 × 0.85 global × 1.3 for a 10-minute video is a $6.63 CPM, and 100,000 views are about $397.80.
• How-toHow do you write a recursive formula for an arithmetic sequence?For 2, 5, 8, 11 the formula is a₁ = 2, aₙ = aₙ₋₁ + 3. The 10th term is 29. The explicit form is aₙ = 2 + (n − 1)(3).
• How-toWhat is the difference between a recursive and an explicit formula?Recursive uses the previous term. Explicit uses n directly. For 2, 5, 8, 11 both give 29 at term 10. A geometric first term of 2 and ratio of 2 gives a 10th term of 1,024. Fibonacci 1, 1, 2, 3, 5 has a 10th term of 55.
• ResearchCalculator search demand benchmarks (2026)Citeable numbers from our Google Search Console export — top impression topics and CTR gaps.

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